added buffer_new_buf() which makes it possible to back a Buffer with an existing pointer without copying

include/pcp/buffer.h

@@ -74,7 +74,7 @@ typedef struct _pcp_buffer Buffer;
 */
 Buffer *buffer_new(size_t blocksize, char *name);
 
-/** Create a new buffer.
+/** Create a new string buffer.
 
     Create a new buffer, initially alloc'd to a blocksize of 32 bytes and zero-filled.
     The buffer will be a string buffer. See buffer_get_str().
@@ -85,6 +85,75 @@ Buffer *buffer_new(size_t blocksize, char *name);
 */
 Buffer *buffer_new_str(char *name);
 
+
+/** Create a new buffer from existing data.
+
+    Create a new buffer, but don't allocate memory nor copy data.
+    Instead the provided data pointer will be used as internal
+    storage directly.
+
+    This kind of buffer can be used to put the Buffer API into
+    use with existing data from other sources. In most cases you'll
+    use it for reading. However, please be aware, that it can be
+    used for writing as well and in this case the data pointer
+    maybe resized (by calling realloc()).
+    
+    When calling buffer_free() on this Buffer, the memory pointed to
+    by the given data pointer will not be free'd and remains accessible.
+    It's the responsibility of the caller to do so.
+
+    Example using mmap(2):
+    @code
+    #include <stdio.h>
+    #include <pcp.h>
+    #include <sys/mman.h>
+
+    FILE *RFD;
+    size_t rs;
+    Buffer *rb;
+    byte *chunk;
+    void *r;
+
+    if((RFD = fopen("README", "rb")) == NULL) {
+      fprintf(stderr, "oops, could not open README!\n");
+      return 1;
+    }
+
+    fseek(RFD, 0, SEEK_END);
+    rs =  ftell(RFD);
+    fseek(RFD, 0, SEEK_SET);
+
+    void *r = mmap(NULL, rs, PROT_READ, 0, fileno(RFD), 0);
+
+    *rb = buffer_new_buf("r", r, rs);
+
+    size_t blocksize = 36;
+    void *chunk = malloc(blocksize);
+
+    while(buffer_done(rb) != 1) {
+      if(buffer_left(rb) < blocksize)
+        blocksize = buffer_left(rb);
+      buffer_get_chunk(rb, chunk, blocksize);
+      _dump("chunk", chunk, blocksize); // or do something else with it
+    }
+
+    buffer_free(rb);
+
+    munmap(r, rs);
+    fclose(RFD);
+    @endcode
+
+    \param[in] name A name for the Buffer. Just used for debugging purposes or in error messages.
+
+    \param[in] data The data pointer to use by the buffer.
+
+    \param[in] datasize The size of the data.
+
+    \return Returns a new Buffer object.
+
+ */
+Buffer *buffer_new_buf(char *name, void *data, size_t datasize);
+
 /* initialize buffer vars */
 void buffer_init(Buffer *b, size_t blocksize, char *name);
 

libpcp/buffer.c

@@ -21,13 +21,6 @@
 
 #include "buffer.h"
 
-Buffer *buffer_new(size_t blocksize, char *name) {
-  Buffer *b = ucmalloc(sizeof(Buffer));
-  b->buf = ucmalloc(blocksize);
-  buffer_init(b, blocksize, name);
-  return b;
-}
-
 void buffer_init(Buffer *b, size_t blocksize, char *name) {
   b->name = ucmalloc(strlen(name)+1);
   b->size = blocksize;
@@ -39,22 +32,39 @@ void buffer_init(Buffer *b, size_t blocksize, char *name) {
   memcpy(b->name, name, strlen(name)+1);
 }
 
+Buffer *buffer_new(size_t blocksize, char *name) {
+  Buffer *b = ucmalloc(sizeof(Buffer));
+  b->buf = ucmalloc(blocksize);
+  buffer_init(b, blocksize, name);
+  return b;
+}
+
 Buffer *buffer_new_str(char *name) {
   Buffer *b = buffer_new(256, name);
   b->isstring = 1;
   return b;
 }
 
+Buffer *buffer_new_buf(char *name, void *data, size_t datasize) {
+  Buffer *b = buffer_new(256, name);
+  b->allocated = 0;
+  b->buf = data;
+  b->size = datasize;
+  b->end = datasize;
+  return b;
+}
+
 void buffer_free(Buffer *b) {
   if(b != NULL) {
     if(b->allocated == 1) {
+      /* free the underlying data pointer only if we allocated it */
       if(b->end > 0) {
 	buffer_clear(b);
+      }
       free(b->buf);
     }
     free(b);
   }
-  }
 }
 
 void buffer_clear(Buffer *b) {

tests/buffertest.c

@@ -1,6 +1,8 @@
 #include "buffertest.h"
+#include <sys/mman.h>
 
 int main() {
+  /* testing basic Buffer api */
   Buffer *test = buffer_new(16, "test");
 
   byte *a = ucmalloc(32);
@@ -52,6 +54,44 @@ int main() {
 
   buffer_free(test);
 
+  /* testing pointer backed buffer */
+  FILE *RFD;
+  size_t rs;
+
+  if((RFD = fopen("README", "rb")) == NULL) {
+    fprintf(stderr, "oops, could not open README!\n");
+    return 1;
+  }
+
+  fseek(RFD, 0, SEEK_END);
+  rs =  ftell(RFD);
+  fseek(RFD, 0, SEEK_SET);
+
+  void *r = mmap(NULL, rs, PROT_READ, 0, fileno(RFD), 0);
+
+  //unsigned char *r = urmalloc(256);
+  Buffer *rb = buffer_new_buf("r", r, rs);
+
+  fprintf(stderr, "r: %p rb->buf: %p\n", r, rb->buf);
+  buffer_info(rb);
+
+  size_t blocksize = 36;
+  void *chunk = malloc(blocksize);
+
+  while(buffer_done(rb) != 1) {
+    if(buffer_left(rb) < blocksize)
+      blocksize = buffer_left(rb);
+    buffer_get_chunk(rb, chunk, blocksize);
+    _dump("chunk", chunk, blocksize);
+  }
+
+  buffer_free(rb);
+
+  _dump("r", r, rs); /* should work! */
+
+  munmap(r, rs);
+  fclose(RFD);
+
   fatals_ifany();
 
   return 0;