webpmux: allow reading argument from a file

if a single text file name is supplied as argument
(e.g.: 'webpmux my_long_list_of_frames.txt'), the command
line arguments are actually parsed from this file.
Tokenizer will remove space, tabs, LF, CR, returns, etc.

+ changed ImgIoUtilReadFile() to return a null-terminated
data, for convenience.

+ misc clean-up in the code

BUG=webp:355

Change-Id: I76796305641d660933de5881763d723006712fa9
---

imageio/imageio_util.c

@@ -47,7 +47,8 @@ int ImgIoUtilReadFromStdin(const uint8_t** data, size_t* data_size) {
   while (!feof(stdin)) {
     // We double the buffer size each time and read as much as possible.
     const size_t extra_size = (max_size == 0) ? kBlockSize : max_size;
-    void* const new_data = realloc(input, max_size + extra_size);
+    // we allocate one extra byte for the \0 terminator
+    void* const new_data = realloc(input, max_size + extra_size + 1);
     if (new_data == NULL) goto Error;
     input = (uint8_t*)new_data;
     max_size += extra_size;
@@ -55,6 +56,7 @@ int ImgIoUtilReadFromStdin(const uint8_t** data, size_t* data_size) {
     if (size < max_size) break;
   }
   if (ferror(stdin)) goto Error;
+  if (input != NULL) input[size] = '\0';  // convenient 0-terminator
   *data = input;
   *data_size = size;
   return 1;
@@ -68,7 +70,7 @@ int ImgIoUtilReadFromStdin(const uint8_t** data, size_t* data_size) {
 int ImgIoUtilReadFile(const char* const file_name,
                       const uint8_t** data, size_t* data_size) {
   int ok;
-  void* file_data;
+  uint8_t* file_data;
   size_t file_size;
   FILE* in;
   const int from_stdin = (file_name == NULL) || !strcmp(file_name, "-");
@@ -87,7 +89,8 @@ int ImgIoUtilReadFile(const char* const file_name,
   fseek(in, 0, SEEK_END);
   file_size = ftell(in);
   fseek(in, 0, SEEK_SET);
-  file_data = malloc(file_size);
+  // we allocate one extra byte for the \0 terminator
+  file_data = (uint8_t*)malloc(file_size + 1);
   if (file_data == NULL) {
     fclose(in);
     fprintf(stderr, "memory allocation failure when reading file %s\n",
@@ -103,11 +106,14 @@ int ImgIoUtilReadFile(const char* const file_name,
     free(file_data);
     return 0;
   }
-  *data = (uint8_t*)file_data;
+  file_data[file_size] = '\0';  // convenient 0-terminator
+  *data = file_data;
   *data_size = file_size;
   return 1;
 }
 
+// -----------------------------------------------------------------------------
+
 int ImgIoUtilWriteFile(const char* const file_name,
                        const uint8_t* data, size_t data_size) {
   int ok;

imageio/imageio_util.h

@@ -30,6 +30,9 @@ FILE* ImgIoUtilSetBinaryMode(FILE* file);
 // Allocates storage for entire file 'file_name' and returns contents and size
 // in 'data' and 'data_size'. Returns 1 on success, 0 otherwise. '*data' should
 // be deleted using free().
+// Note: for convenience, the data will be null-terminated with an extra byte
+// (not accounted for in *data_size), in case the file is text and intended
+// to be used as a C-string.
 // If 'file_name' is NULL or equal to "-", input is read from stdin by calling
 // the function ImgIoUtilReadFromStdin().
 int ImgIoUtilReadFile(const char* const file_name,