Move examples into subfolders, add READMEs

examples/network_server/Makefile

@@ -0,0 +1,19 @@
+CFLAGS = -ansi -Wall -Werror -g -O0
+
+# Path to the nanopb root folder
+NANOPB_DIR = ../..
+DEPS = $(NANOPB_DIR)/pb_decode.c $(NANOPB_DIR)/pb_decode.h \
+       $(NANOPB_DIR)/pb_encode.c $(NANOPB_DIR)/pb_encode.h $(NANOPB_DIR)/pb.h
+CFLAGS += -I$(NANOPB_DIR)
+
+all: server client
+
+clean:
+	rm -f server client fileproto.pb.c fileproto.pb.h
+
+%: %.c $(DEPS) fileproto.pb.h fileproto.pb.c
+	$(CC) $(CFLAGS) -o $@ $< $(NANOPB_DIR)/pb_decode.c $(NANOPB_DIR)/pb_encode.c fileproto.pb.c common.c
+
+fileproto.pb.c fileproto.pb.h: fileproto.proto $(NANOPB_DIR)/generator/nanopb_generator.py
+	protoc -ofileproto.pb $<
+	python $(NANOPB_DIR)/generator/nanopb_generator.py fileproto.pb

examples/network_server/README

@@ -0,0 +1,60 @@
+Nanopb example "network_server"
+===============================
+
+This example demonstrates the use of nanopb to communicate over network
+connections. It consists of a server that sends file listings, and of
+a client that requests the file list from the server.
+
+Example usage
+-------------
+
+user@host:~/nanopb/examples/network_server$ make        # Build the example
+protoc -ofileproto.pb fileproto.proto
+python ../../generator/nanopb_generator.py fileproto.pb
+Writing to fileproto.pb.h and fileproto.pb.c
+cc -ansi -Wall -Werror -I .. -g -O0 -I../.. -o server server.c
+    ../../pb_decode.c ../../pb_encode.c fileproto.pb.c common.c
+cc -ansi -Wall -Werror -I .. -g -O0 -I../.. -o client client.c
+    ../../pb_decode.c ../../pb_encode.c fileproto.pb.c common.c
+
+user@host:~/nanopb/examples/network_server$ ./server &  # Start the server on background
+[1] 24462
+
+petteri@oddish:~/nanopb/examples/network_server$ ./client /bin  # Request the server to list /bin
+Got connection.
+Listing directory: /bin
+1327119    bzdiff
+1327126    bzless
+1327147    ps
+1327178    ntfsmove
+1327271    mv
+1327187    mount
+1327259    false
+1327266    tempfile
+1327285    zfgrep
+1327165    gzexe
+1327204    nc.openbsd
+1327260    uname
+
+
+Details of implementation
+-------------------------
+fileproto.proto contains the portable Google Protocol Buffers protocol definition.
+It could be used as-is to implement a server or a client in any other language, for
+example Python or Java.
+
+fileproto.options contains the nanopb-specific options for the protocol file. This
+sets the amount of space allocated for file names when decoding messages.
+
+common.c/h contains functions that allow nanopb to read and write directly from
+network socket. This way there is no need to allocate a separate buffer to store
+the message.
+
+server.c contains the code to open a listening socket, to respond to clients and
+to list directory contents.
+
+client.c contains the code to connect to a server, to send a request and to print
+the response message.
+
+The code is implemented using the POSIX socket api, but it should be easy enough
+to port into any other socket api, such as lwip.

examples/network_server/client.c

@@ -0,0 +1,116 @@
+/* This is a simple TCP client that connects to port 1234 and prints a list
+ * of files in a given directory.
+ *
+ * It directly deserializes and serializes messages from network, minimizing
+ * memory use.
+ * 
+ * For flexibility, this example is implemented using posix api.
+ * In a real embedded system you would typically use some other kind of
+ * a communication and filesystem layer.
+ */
+
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <netinet/in.h>
+#include <unistd.h>
+#include <dirent.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <pb_encode.h>
+#include <pb_decode.h>
+
+#include "fileproto.pb.h"
+#include "common.h"
+
+bool printfile_callback(pb_istream_t *stream, const pb_field_t *field, void **arg)
+{
+    FileInfo fileinfo;
+    
+    if (!pb_decode(stream, FileInfo_fields, &fileinfo))
+        return false;
+    
+    printf("%-10lld %s\n", (long long)fileinfo.inode, fileinfo.name);
+    
+    return true;
+}
+
+bool listdir(int fd, char *path)
+{
+    ListFilesRequest request;
+    ListFilesResponse response;
+    pb_istream_t input = pb_istream_from_socket(fd);
+    pb_ostream_t output = pb_ostream_from_socket(fd);
+    uint8_t zero = 0;
+    
+    if (path == NULL)
+    {
+        request.has_path = false;
+    }
+    else
+    {
+        request.has_path = true;
+        if (strlen(path) + 1 > sizeof(request.path))
+        {
+            fprintf(stderr, "Too long path.\n");
+            return false;
+        }
+        
+        strcpy(request.path, path);
+    }
+    
+    if (!pb_encode(&output, ListFilesRequest_fields, &request))
+    {
+        fprintf(stderr, "Encoding failed.\n");
+        return false;
+    }
+    
+    /* We signal the end of request with a 0 tag. */
+    pb_write(&output, &zero, 1);
+    
+    response.file.funcs.decode = &printfile_callback;
+    
+    if (!pb_decode(&input, ListFilesResponse_fields, &response))
+    {
+        fprintf(stderr, "Decode failed: %s\n", PB_GET_ERROR(&input));
+        return false;
+    }
+    
+    if (response.path_error)
+    {
+        fprintf(stderr, "Server reported error.\n");
+        return false;
+    }
+    
+    return true;
+}
+
+int main(int argc, char **argv)
+{
+    int sockfd;
+    struct sockaddr_in servaddr;
+    char *path = NULL;
+    
+    if (argc > 1)
+        path = argv[1];
+    
+    sockfd = socket(AF_INET, SOCK_STREAM, 0);
+    
+    memset(&servaddr, 0, sizeof(servaddr));
+    servaddr.sin_family = AF_INET;
+    servaddr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+    servaddr.sin_port = htons(1234);
+    
+    if (connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) != 0)
+    {
+        perror("connect");
+        return 1;
+    }
+    
+    if (!listdir(sockfd, path))
+        return 2;
+    
+    close(sockfd);
+    
+    return 0;
+}

examples/network_server/common.c

@@ -0,0 +1,40 @@
+/* Simple binding of nanopb streams to TCP sockets.
+ */
+
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <pb_encode.h>
+#include <pb_decode.h>
+
+#include "common.h"
+
+static bool write_callback(pb_ostream_t *stream, const uint8_t *buf, size_t count)
+{
+    int fd = (intptr_t)stream->state;
+    return send(fd, buf, count, 0) == count;
+}
+
+static bool read_callback(pb_istream_t *stream, uint8_t *buf, size_t count)
+{
+    int fd = (intptr_t)stream->state;
+    int result;
+    
+    result = recv(fd, buf, count, MSG_WAITALL);
+    
+    if (result == 0)
+        stream->bytes_left = 0; /* EOF */
+    
+    return result == count;
+}
+
+pb_ostream_t pb_ostream_from_socket(int fd)
+{
+    pb_ostream_t stream = {&write_callback, (void*)(intptr_t)fd, SIZE_MAX, 0};
+    return stream;
+}
+
+pb_istream_t pb_istream_from_socket(int fd)
+{
+    pb_istream_t stream = {&read_callback, (void*)(intptr_t)fd, SIZE_MAX};
+    return stream;
+}

examples/network_server/common.h

@@ -0,0 +1,9 @@
+#ifndef _PB_EXAMPLE_COMMON_H_
+#define _PB_EXAMPLE_COMMON_H_
+
+#include <pb.h>
+
+pb_ostream_t pb_ostream_from_socket(int fd);
+pb_istream_t pb_istream_from_socket(int fd);
+
+#endif

examples/network_server/fileproto.options

@@ -0,0 +1,13 @@
+# This file defines the nanopb-specific options for the messages defined
+# in fileproto.proto.
+#
+# If you come from high-level programming background, the hardcoded
+# maximum lengths may disgust you. However, if your microcontroller only
+# has a few kB of ram to begin with, setting reasonable limits for
+# filenames is ok.
+#
+# On the other hand, using the callback interface, it is not necessary
+# to set a limit on the number of files in the response.
+
+ListFilesRequest.path 	max_size:128
+FileInfo.name 		max_size:128

examples/network_server/fileproto.proto

@@ -0,0 +1,18 @@
+// This defines protocol for a simple server that lists files.
+//
+// See also the nanopb-specific options in fileproto.options.
+
+message ListFilesRequest {
+    optional string path = 1 [default = "/"];
+}
+
+message FileInfo {
+    required uint64 inode = 1;
+    required string name = 2;
+}
+
+message ListFilesResponse {
+    optional bool path_error = 1 [default = false];
+    repeated FileInfo file = 2;
+}
+

examples/network_server/server.c

@@ -0,0 +1,131 @@
+/* This is a simple TCP server that listens on port 1234 and provides lists
+ * of files to clients, using a protocol defined in file_server.proto.
+ *
+ * It directly deserializes and serializes messages from network, minimizing
+ * memory use.
+ * 
+ * For flexibility, this example is implemented using posix api.
+ * In a real embedded system you would typically use some other kind of
+ * a communication and filesystem layer.
+ */
+
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <netinet/in.h>
+#include <unistd.h>
+#include <dirent.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <pb_encode.h>
+#include <pb_decode.h>
+
+#include "fileproto.pb.h"
+#include "common.h"
+
+bool listdir_callback(pb_ostream_t *stream, const pb_field_t *field, void * const *arg)
+{
+    DIR *dir = (DIR*) *arg;
+    struct dirent *file;
+    FileInfo fileinfo;
+    
+    while ((file = readdir(dir)) != NULL)
+    {
+        fileinfo.inode = file->d_ino;
+        strncpy(fileinfo.name, file->d_name, sizeof(fileinfo.name));
+        fileinfo.name[sizeof(fileinfo.name) - 1] = '\0';
+        
+        if (!pb_encode_tag_for_field(stream, field))
+            return false;
+        
+        if (!pb_encode_submessage(stream, FileInfo_fields, &fileinfo))
+            return false;
+    }
+    
+    return true;
+}
+
+void handle_connection(int connfd)
+{
+    ListFilesRequest request;
+    ListFilesResponse response;
+    pb_istream_t input = pb_istream_from_socket(connfd);
+    pb_ostream_t output = pb_ostream_from_socket(connfd);
+    DIR *directory;
+    
+    if (!pb_decode(&input, ListFilesRequest_fields, &request))
+    {
+        printf("Decode failed: %s\n", PB_GET_ERROR(&input));
+        return;
+    }
+    
+    directory = opendir(request.path);
+    
+    printf("Listing directory: %s\n", request.path);
+    
+    if (directory == NULL)
+    {
+        perror("opendir");
+        
+        response.has_path_error = true;
+        response.path_error = true;
+        response.file.funcs.encode = NULL;
+    }
+    else
+    {
+        response.has_path_error = false;
+        response.file.funcs.encode = &listdir_callback;
+        response.file.arg = directory;
+    }
+    
+    if (!pb_encode(&output, ListFilesResponse_fields, &response))
+    {
+        printf("Encoding failed.\n");
+    }
+}
+
+int main(int argc, char **argv)
+{
+    int listenfd, connfd;
+    struct sockaddr_in servaddr;
+    int reuse = 1;
+    
+    listenfd = socket(AF_INET, SOCK_STREAM, 0);
+    
+    setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse));
+    
+    memset(&servaddr, 0, sizeof(servaddr));
+    servaddr.sin_family = AF_INET;
+    servaddr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+    servaddr.sin_port = htons(1234);
+    if (bind(listenfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) != 0)
+    {
+        perror("bind");
+        return 1;
+    }
+    
+    if (listen(listenfd, 5) != 0)
+    {
+        perror("listen");
+        return 1;
+    }
+    
+    for(;;)
+    {
+        connfd = accept(listenfd, NULL, NULL);
+        
+        if (connfd < 0)
+        {
+            perror("accept");
+            return 1;
+        }
+        
+        printf("Got connection.\n");
+        
+        handle_connection(connfd);
+        
+        printf("Closing connection.\n");
+        
+        close(connfd);
+    }
+}

examples/using_double_on_avr/Makefile

@@ -0,0 +1,29 @@
+CFLAGS = -Wall -Werror -g -O0
+
+# Path to the nanopb root directory
+NANOPB_DIR = ../..
+DEPS = double_conversion.c $(NANOPB_DIR)/pb.h \
+	$(NANOPB_DIR)/pb_decode.c $(NANOPB_DIR)/pb_decode.h \
+	$(NANOPB_DIR)/pb_encode.c $(NANOPB_DIR)/pb_encode.h
+CFLAGS += -I$(NANOPB_DIR)
+
+all: run_tests
+
+clean:
+	rm -f test_conversions encode_double decode_double doubleproto.pb.c doubleproto.pb.h
+
+test_conversions: test_conversions.c double_conversion.c
+	$(CC) $(CFLAGS) -o $@ $^
+
+%: %.c $(DEPS) doubleproto.pb.h doubleproto.pb.c
+	$(CC) $(CFLAGS) -o $@ $< double_conversion.c \
+		$(NANOPB_DIR)/pb_decode.c $(NANOPB_DIR)/pb_encode.c doubleproto.pb.c
+
+doubleproto.pb.c doubleproto.pb.h: doubleproto.proto $(NANOPB_DIR)/generator/nanopb_generator.py
+	protoc -odoubleproto.pb $<
+	python $(NANOPB_DIR)/generator/nanopb_generator.py doubleproto.pb
+
+run_tests: test_conversions encode_double decode_double
+	./test_conversions
+	./encode_double | ./decode_double
+    

examples/using_double_on_avr/README

@@ -0,0 +1,25 @@
+Nanopb example "using_double_on_avr"
+====================================
+
+Some processors/compilers, such as AVR-GCC, do not support the double
+datatype. Instead, they have sizeof(double) == 4. Because protocol
+binary format uses the double encoding directly, this causes trouble
+if the protocol in .proto requires double fields.
+
+This directory contains a solution to this problem. It uses uint64_t
+to store the raw wire values, because its size is correct on all
+platforms. The file double_conversion.c provides functions that
+convert these values to/from floats, without relying on compiler
+support.
+
+To use this method, you need to make some modifications to your code:
+
+1) Change all 'double' fields into 'fixed64' in the .proto.
+
+2) Whenever writing to a 'double' field, use float_to_double().
+
+3) Whenever reading a 'double' field, use double_to_float().
+
+The conversion routines are as accurate as the float datatype can
+be. Furthermore, they should handle all special values (NaN, inf, denormalized
+numbers) correctly. There are testcases in test_conversions.c.

examples/using_double_on_avr/decode_double.c

@@ -0,0 +1,33 @@
+/* Decodes a double value into a float variable.
+ * Used to read double values with AVR code, which doesn't support double directly.
+ */
+
+#include <stdio.h>
+#include <pb_decode.h>
+#include "double_conversion.h"
+#include "doubleproto.pb.h"
+
+int main()
+{
+    uint8_t buffer[32];
+    size_t count = fread(buffer, 1, sizeof(buffer), stdin);
+    pb_istream_t stream = pb_istream_from_buffer(buffer, count);
+    
+    AVRDoubleMessage message;
+    pb_decode(&stream, AVRDoubleMessage_fields, &message);
+    
+    float v1 = double_to_float(message.field1);
+    float v2 = double_to_float(message.field2);
+
+    printf("Values: %f %f\n", v1, v2);
+    
+    if (v1 == 1234.5678f &&
+        v2 == 0.00001f)
+    {
+        return 0;
+    }
+    else
+    {
+        return 1;
+    }
+}

examples/using_double_on_avr/double_conversion.c

@@ -0,0 +1,123 @@
+/* Conversion routines for platforms that do not support 'double' directly. */
+
+#include "double_conversion.h"
+#include <math.h>
+
+typedef union {
+    float f;
+    uint32_t i;
+} conversion_t;
+
+/* Note: IEE 754 standard specifies float formats as follows:
+ * Single precision: sign,  8-bit exp, 23-bit frac.
+ * Double precision: sign, 11-bit exp, 52-bit frac.
+ */
+
+uint64_t float_to_double(float value)
+{
+    conversion_t in;
+    in.f = value;
+    uint8_t sign;
+    int16_t exponent;
+    uint64_t mantissa;
+    
+    /* Decompose input value */
+    sign = (in.i >> 31) & 1;
+    exponent = ((in.i >> 23) & 0xFF) - 127;
+    mantissa = in.i & 0x7FFFFF;
+    
+    if (exponent == 128)
+    {
+        /* Special value (NaN etc.) */
+        exponent = 1024;
+    }
+    else if (exponent == -127)
+    {
+        if (!mantissa)
+        {
+            /* Zero */
+            exponent = -1023;
+        }
+        else
+        {
+            /* Denormalized */
+            mantissa <<= 1;
+            while (!(mantissa & 0x800000))
+            {
+                mantissa <<= 1;
+                exponent--;
+            }
+            mantissa &= 0x7FFFFF;
+        }
+    }
+    
+    /* Combine fields */
+    mantissa <<= 29;
+    mantissa |= (uint64_t)(exponent + 1023) << 52;
+    mantissa |= (uint64_t)sign << 63;
+    
+    return mantissa;
+}
+
+float double_to_float(uint64_t value)
+{
+    uint8_t sign;
+    int16_t exponent;
+    uint32_t mantissa;
+    conversion_t out;
+
+    /* Decompose input value */
+    sign = (value >> 63) & 1;
+    exponent = ((value >> 52) & 0x7FF) - 1023;
+    mantissa = (value >> 28) & 0xFFFFFF; /* Highest 24 bits */
+ 
+    /* Figure if value is in range representable by floats. */
+    if (exponent == 1024)
+    {
+        /* Special value */
+        exponent = 128;
+    }
+    else if (exponent > 127)
+    {
+        /* Too large */        
+        if (sign)
+            return -INFINITY;
+        else
+            return INFINITY;
+    }
+    else if (exponent < -150)
+    {
+        /* Too small */
+        if (sign)
+            return -0.0f;
+        else
+            return 0.0f;
+    }
+    else if (exponent < -126)
+    {
+        /* Denormalized */
+        mantissa |= 0x1000000;
+        mantissa >>= (-126 - exponent);
+        exponent = -127;
+    }
+ 
+    /* Round off mantissa */
+    mantissa = (mantissa + 1) >> 1;
+    
+    /* Check if mantissa went over 2.0 */
+    if (mantissa & 0x800000)
+    {
+        exponent += 1;
+        mantissa &= 0x7FFFFF;
+        mantissa >>= 1;
+    }
+    
+    /* Combine fields */
+    out.i = mantissa;
+    out.i |= (uint32_t)(exponent + 127) << 23;
+    out.i |= (uint32_t)sign << 31;
+    
+    return out.f;
+}
+
+

examples/using_double_on_avr/double_conversion.h

@@ -0,0 +1,26 @@
+/* AVR-GCC does not have real double datatype. Instead its double
+ * is equal to float, i.e. 32 bit value. If you need to communicate
+ * with other systems that use double in their .proto files, you
+ * need to do some conversion.
+ *
+ * These functions use bitwise operations to mangle floats into doubles
+ * and then store them in uint64_t datatype.
+ */
+
+#ifndef DOUBLE_CONVERSION
+#define DOUBLE_CONVERSION
+
+#include <stdint.h>
+
+/* Convert native 4-byte float into a 8-byte double. */
+extern uint64_t float_to_double(float value);
+
+/* Convert 8-byte double into native 4-byte float.
+ * Values are rounded to nearest, 0.5 away from zero.
+ * Overflowing values are converted to Inf or -Inf.
+ */
+extern float double_to_float(uint64_t value);
+
+
+#endif
+

examples/using_double_on_avr/doubleproto.proto

@@ -0,0 +1,13 @@
+// A message containing doubles, as used by other applications.
+message DoubleMessage {
+    required double field1 = 1;
+    required double field2 = 2;
+}
+
+// A message containing doubles, but redefined using uint64_t.
+// For use in AVR code.
+message AVRDoubleMessage {
+    required fixed64 field1 = 1;
+    required fixed64 field2 = 2;
+}
+

examples/using_double_on_avr/encode_double.c

@@ -0,0 +1,25 @@
+/* Encodes a float value into a double on the wire.
+ * Used to emit doubles from AVR code, which doesn't support double directly.
+ */
+
+#include <stdio.h>
+#include <pb_encode.h>
+#include "double_conversion.h"
+#include "doubleproto.pb.h"
+
+int main()
+{
+    AVRDoubleMessage message = {
+        float_to_double(1234.5678f),
+        float_to_double(0.00001f)
+    };
+    
+    uint8_t buffer[32];
+    pb_ostream_t stream = pb_ostream_from_buffer(buffer, sizeof(buffer));
+    
+    pb_encode(&stream, AVRDoubleMessage_fields, &message);
+    fwrite(buffer, 1, stream.bytes_written, stdout);
+
+    return 0;
+}
+

examples/using_double_on_avr/test_conversions.c

@@ -0,0 +1,56 @@
+#include "double_conversion.h"
+#include <math.h>
+#include <stdio.h>
+
+static const double testvalues[] = {
+           0.0,        -0.0,         0.1,         -0.1,
+          M_PI,       -M_PI,  123456.789,  -123456.789,
+      INFINITY,   -INFINITY,         NAN, INFINITY - INFINITY,
+          1e38,       -1e38,        1e39,        -1e39,
+         1e-38,      -1e-38,       1e-39,       -1e-39,
+   3.14159e-37,-3.14159e-37, 3.14159e-43, -3.14159e-43,
+         1e-60,      -1e-60,       1e-45,       -1e-45,
+    0.99999999999999, -0.99999999999999, 127.999999999999, -127.999999999999
+};
+
+#define TESTVALUES_COUNT (sizeof(testvalues)/sizeof(testvalues[0]))
+
+int main()
+{
+    int status = 0;
+    int i;
+    for (i = 0; i < TESTVALUES_COUNT; i++)
+    {
+        double orig = testvalues[i];
+        float expected_float = (float)orig;
+        double expected_double = (double)expected_float;
+        
+        float got_float = double_to_float(*(uint64_t*)&orig);
+        uint64_t got_double = float_to_double(got_float);
+        
+        uint32_t e1 = *(uint32_t*)&expected_float;
+        uint32_t g1 = *(uint32_t*)&got_float;
+        uint64_t e2 = *(uint64_t*)&expected_double;
+        uint64_t g2 = got_double;
+        
+        if (g1 != e1)
+        {
+            printf("%3d double_to_float fail: %08x != %08x\n", i, g1, e1);
+            status = 1;
+        }
+        
+        if (g2 != e2)
+        {
+            printf("%3d float_to_double fail: %016llx != %016llx\n", i,
+                (unsigned long long)g2,
+                (unsigned long long)e2);
+            status = 1;
+        }
+    }
+
+    return status;
+}
+
+    
+    
+

examples/using_union_messages/Makefile

@@ -0,0 +1,22 @@
+CFLAGS = -ansi -Wall -Werror -g -O0
+
+# Path to the nanopb root folder
+NANOPB_DIR = ../..
+DEPS = $(NANOPB_DIR)/pb_decode.c $(NANOPB_DIR)/pb_decode.h \
+       $(NANOPB_DIR)/pb_encode.c $(NANOPB_DIR)/pb_encode.h $(NANOPB_DIR)/pb.h
+CFLAGS += -I$(NANOPB_DIR)
+
+all: encode decode
+	./encode 1 | ./decode
+	./encode 2 | ./decode
+	./encode 3 | ./decode
+
+clean:
+	rm -f encode unionproto.pb.h unionproto.pb.c
+
+%: %.c $(DEPS) unionproto.pb.h unionproto.pb.c
+	$(CC) $(CFLAGS) -o $@ $< $(NANOPB_DIR)/pb_decode.c $(NANOPB_DIR)/pb_encode.c unionproto.pb.c
+
+unionproto.pb.h unionproto.pb.c: unionproto.proto $(NANOPB_DIR)/generator/nanopb_generator.py
+	protoc -ounionproto.pb $<
+	python $(NANOPB_DIR)/generator/nanopb_generator.py unionproto.pb

examples/using_union_messages/README

@@ -0,0 +1,52 @@
+Nanopb example "using_union_messages"
+=====================================
+
+Union messages is a common technique in Google Protocol Buffers used to
+represent a group of messages, only one of which is passed at a time.
+It is described in Google's documentation:
+https://developers.google.com/protocol-buffers/docs/techniques#union
+
+This directory contains an example on how to encode and decode union messages
+with minimal memory usage. Usually, nanopb would allocate space to store
+all of the possible messages at the same time, even though at most one of
+them will be used at a time.
+
+By using some of the lower level nanopb APIs, we can manually generate the
+top level message, so that we only need to allocate the one submessage that
+we actually want. Similarly when decoding, we can manually read the tag of
+the top level message, and only then allocate the memory for the submessage
+after we already know its type.
+
+
+Example usage
+-------------
+
+Type `make` to run the example. It will build it and run commands like
+following:
+
+./encode 1 | ./decode
+Got MsgType1: 42
+./encode 2 | ./decode
+Got MsgType2: true
+./encode 3 | ./decode
+Got MsgType3: 3 1415
+
+This simply demonstrates that the "decode" program has correctly identified
+the type of the received message, and managed to decode it.
+
+
+Details of implementation
+-------------------------
+
+unionproto.proto contains the protocol used in the example. It consists of
+three messages: MsgType1, MsgType2 and MsgType3, which are collected together
+into UnionMessage.
+
+encode.c takes one command line argument, which should be a number 1-3. It
+then fills in and encodes the corresponding message, and writes it to stdout.
+
+decode.c reads a UnionMessage from stdin. Then it calls the function
+decode_unionmessage_type() to determine the type of the message. After that,
+the corresponding message is decoded and the contents of it printed to the
+screen.
+

examples/using_union_messages/decode.c

@@ -0,0 +1,96 @@
+/* This program reads a message from stdin, detects its type and decodes it.
+ */
+ 
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include <pb_decode.h>
+#include "unionproto.pb.h"
+
+/* This function reads manually the first tag from the stream and finds the
+ * corresponding message type. It doesn't yet decode the actual message.
+ *
+ * Returns a pointer to the MsgType_fields array, as an identifier for the
+ * message type. Returns null if the tag is of unknown type or an error occurs.
+ */
+const pb_field_t* decode_unionmessage_type(pb_istream_t *stream)
+{
+    pb_wire_type_t wire_type;
+    uint32_t tag;
+    bool eof;
+
+    while (pb_decode_tag(stream, &wire_type, &tag, &eof))
+    {
+        if (wire_type == PB_WT_STRING)
+        {
+            const pb_field_t *field;
+            for (field = UnionMessage_fields; field->tag != 0; field++)
+            {
+                if (field->tag == tag && (field->type & PB_LTYPE_SUBMESSAGE))
+                {
+                    /* Found our field. */
+                    return field->ptr;
+                }
+            }
+        }
+        
+        /* Wasn't our field.. */
+        pb_skip_field(stream, wire_type);
+    }
+    
+    return NULL;
+}
+
+bool decode_unionmessage_contents(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct)
+{
+    pb_istream_t substream;
+    bool status;
+    if (!pb_make_string_substream(stream, &substream))
+        return false;
+    
+    status = pb_decode(&substream, fields, dest_struct);
+    pb_close_string_substream(stream, &substream);
+    return status;
+}
+
+int main()
+{
+    /* Read the data into buffer */
+    uint8_t buffer[512];
+    size_t count = fread(buffer, 1, sizeof(buffer), stdin);
+    pb_istream_t stream = pb_istream_from_buffer(buffer, count);
+    
+    const pb_field_t *type = decode_unionmessage_type(&stream);
+    bool status = false;
+    
+    if (type == MsgType1_fields)
+    {
+        MsgType1 msg = {};
+        status = decode_unionmessage_contents(&stream, MsgType1_fields, &msg);
+        printf("Got MsgType1: %d\n", msg.value);
+    }
+    else if (type == MsgType2_fields)
+    {
+        MsgType2 msg = {};
+        status = decode_unionmessage_contents(&stream, MsgType2_fields, &msg);
+        printf("Got MsgType2: %s\n", msg.value ? "true" : "false");
+    }
+    else if (type == MsgType3_fields)
+    {
+        MsgType3 msg = {};
+        status = decode_unionmessage_contents(&stream, MsgType3_fields, &msg);
+        printf("Got MsgType3: %d %d\n", msg.value1, msg.value2);    
+    }
+    
+    if (!status)
+    {
+        printf("Decode failed: %s\n", PB_GET_ERROR(&stream));
+        return 1;
+    }
+    
+    return 0;
+}
+
+
+

examples/using_union_messages/encode.c

@@ -0,0 +1,85 @@
+/* This program takes a command line argument and encodes a message in
+ * one of MsgType1, MsgType2 or MsgType3.
+ */
+ 
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include <pb_encode.h>
+#include "unionproto.pb.h"
+
+/* This function is the core of the union encoding process. It handles
+ * the top-level pb_field_t array manually, in order to encode a correct
+ * field tag before the message. The pointer to MsgType_fields array is
+ * used as an unique identifier for the message type.
+ */
+bool encode_unionmessage(pb_ostream_t *stream, const pb_field_t messagetype[], const void *message)
+{
+    const pb_field_t *field;
+    for (field = UnionMessage_fields; field->tag != 0; field++)
+    {
+        if (field->ptr == messagetype)
+        {
+            /* This is our field, encode the message using it. */
+            if (!pb_encode_tag_for_field(stream, field))
+                return false;
+            
+            return pb_encode_submessage(stream, messagetype, message);
+        }
+    }
+    
+    /* Didn't find the field for messagetype */
+    return false;
+}
+
+int main(int argc, char **argv)
+{
+    if (argc != 2)
+    {
+        fprintf(stderr, "Usage: %s (1|2|3)\n", argv[0]);
+        return 1;
+    }
+    
+    uint8_t buffer[512];
+    pb_ostream_t stream = pb_ostream_from_buffer(buffer, sizeof(buffer));
+    
+    bool status = false;
+    int msgtype = atoi(argv[1]);
+    if (msgtype == 1)
+    {
+        /* Send message of type 1 */
+        MsgType1 msg = {42};
+        status = encode_unionmessage(&stream, MsgType1_fields, &msg);
+    }
+    else if (msgtype == 2)
+    {
+        /* Send message of type 2 */
+        MsgType2 msg = {true};
+        status = encode_unionmessage(&stream, MsgType2_fields, &msg);
+    }
+    else if (msgtype == 3)
+    {
+        /* Send message of type 3 */
+        MsgType3 msg = {3, 1415};
+        status = encode_unionmessage(&stream, MsgType3_fields, &msg);
+    }
+    else
+    {
+        fprintf(stderr, "Unknown message type: %d\n", msgtype);
+        return 2;
+    }
+    
+    if (!status)
+    {
+        fprintf(stderr, "Encoding failed!\n");
+        return 3;
+    }
+    else
+    {
+        fwrite(buffer, 1, stream.bytes_written, stdout);
+        return 0; /* Success */
+    }
+}
+
+

examples/using_union_messages/unionproto.proto

@@ -0,0 +1,30 @@
+// This is an example of how to handle 'union' style messages
+// with nanopb, without allocating memory for all the message types.
+//
+// There is no official type in Protocol Buffers for describing unions,
+// but they are commonly implemented by filling out exactly one of
+// several optional fields.
+
+message MsgType1
+{
+    required int32 value = 1;
+}
+
+message MsgType2
+{
+    required bool value = 1;
+}
+
+message MsgType3
+{
+    required int32 value1 = 1;
+    required int32 value2 = 2;
+}
+
+message UnionMessage
+{
+    optional MsgType1 msg1 = 1;
+    optional MsgType2 msg2 = 2;
+    optional MsgType3 msg3 = 3;
+}
+