Bug 1806394 r=nalexander

Differential Revision: https://phabricator.services.mozilla.com/D168294

modules/libmar/src/mar.h

@@ -55,7 +55,8 @@ typedef struct SeenIndex_ {
  * Mozilla ARchive (MAR) file data structure
  */
 struct MarFile_ {
-  FILE* fp;                       /* file pointer to the archive */
+  unsigned char* buffer;          /* file buffer containing the entire MAR */
+  size_t data_len;                /* byte count of the data in the buffer */
   MarItem* item_table[TABLESIZE]; /* hash table of files in the archive */
   SeenIndex* index_list;          /* file indexes processed */
   int item_table_is_valid;        /* header and index validation flag */
@@ -72,16 +73,29 @@ typedef struct MarFile_ MarFile;
  */
 typedef int (*MarItemCallback)(MarFile* mar, const MarItem* item, void* data);
 
+enum MarReadResult_ {
+  MAR_READ_SUCCESS,
+  MAR_IO_ERROR,
+  MAR_MEM_ERROR,
+  MAR_FILE_TOO_BIG_ERROR,
+};
+
+typedef enum MarReadResult_ MarReadResult;
+
 /**
  * Open a MAR file for reading.
  * @param path      Specifies the path to the MAR file to open.  This path must
  *                  be compatible with fopen.
+ * @param out_mar   Out-parameter through which the created MarFile structure is
+ *                  returned. Guaranteed to be a valid structure if
+ *                  MAR_READ_SUCCESS is returned. Otherwise NULL will be
+ *                  assigned.
  * @return          NULL if an error occurs.
  */
-MarFile* mar_open(const char* path);
+MarReadResult mar_open(const char* path, MarFile** out_mar);
 
 #ifdef XP_WIN
-MarFile* mar_wopen(const wchar_t* path);
+MarReadResult mar_wopen(const wchar_t* path, MarFile** out_mar);
 #endif
 
 /**
@@ -90,6 +104,49 @@ MarFile* mar_wopen(const wchar_t* path);
  */
 void mar_close(MarFile* mar);
 
+/**
+ * Reads the specified amount of data from the buffer in MarFile that contains
+ * the entirety of the MAR file data.
+ * @param mar       The MAR file to read from.
+ * @param dest      The buffer to read into.
+ * @param position  The byte index to start reading from the MAR at.
+ *                  On success, position will be incremented by size.
+ * @param size      The number of bytes to read.
+ * @return          0  If the specified amount of data was read.
+ *                  -1 If the buffer MAR is not large enough to read the
+ *                     specified amount of data at the specified position.
+ */
+int mar_read_buffer(MarFile* mar, void* dest, size_t* position, size_t size);
+
+/**
+ * Reads the specified amount of data from the buffer in MarFile that contains
+ * the entirety of the MAR file data. If there isn't that much data remaining,
+ * reads as much as possible.
+ * @param mar       The MAR file to read from.
+ * @param dest      The buffer to read into.
+ * @param position  The byte index to start reading from the MAR at.
+ *                  This function will increment position by the number of bytes
+ *                  copied.
+ * @param size      The maximum number of bytes to read.
+ * @return          The number of bytes copied into dest.
+ */
+int mar_read_buffer_max(MarFile* mar, void* dest, size_t* position,
+                        size_t size);
+
+/**
+ * Increments position by distance. Checks that the resulting position is still
+ * within the bounds of the buffer. Much like fseek, this will allow position to
+ * be successfully placed just after the end of the buffer.
+ * @param mar       The MAR file to read from.
+ * @param position  The byte index to start reading from the MAR at.
+ *                  On success, position will be incremented by size.
+ * @param distance  The number of bytes to move forward by.
+ * @return          0  If position was successfully moved.
+ *                  -1 If moving position by distance would move it outside the
+ *                     bounds of the buffer.
+ */
+int mar_buffer_seek(MarFile* mar, size_t* position, size_t distance);
+
 /**
  * Find an item in the MAR file by name.
  * @param mar       The MarFile object to query.

modules/libmar/src/mar_extract.c

@@ -75,8 +75,8 @@ int mar_extract(const char* path) {
   MarFile* mar;
   int rv;
 
-  mar = mar_open(path);
-  if (!mar) {
+  MarReadResult result = mar_open(path, &mar);
+  if (result != MAR_READ_SUCCESS) {
     return -1;
   }