Add ring implementation

include/ring.h

@@ -0,0 +1,54 @@
+#ifndef __HALO_INCLUDE_RING_
+#define __HALO_INCLUDE_RING_
+
+#include <stddef.h>
+
+/*
+ * circular ring buffer for continous reading and writing
+ */
+
+struct ring_t {
+  /*
+   * the current length of the unread data in the buffer
+   */
+
+  size_t buflen;
+
+  /*
+   * the full buffer
+   */
+
+  char *buffer;
+
+  /*
+   * the beginning of the full buffer
+   */
+
+  char *begin;
+
+  /*
+   * the ending of the full buffer
+   */
+
+  char *end;
+
+  /*
+   * the beginning of the unread data in the buffer
+   */
+
+  char *reader;
+
+  /*
+   * the end of the unread data in the buffer
+   */
+
+  char *writer;
+};
+
+struct ring_t *ring_new(struct ring_t *buf, size_t len);
+size_t ring_write(struct ring_t *buf, char *str, size_t orig_len);
+char *ring_read(struct ring_t *buf, size_t *len);
+char *ring_readln(struct ring_t *buf, size_t *len);
+void ring_del(struct ring_t *buf);
+
+#endif

src/ring.c

@@ -0,0 +1,159 @@
+#include <ring.h>
+#include <stdlib.h>
+
+/*
+ * ring_new
+ * build a new ring buffer object
+ *
+ * parameters:
+ *   struct ring_t *buf - ring object (provided by user)
+ *   size_t len - length to build the buffer
+ *
+ * returns the ring object (buf) or NULL if there is an error
+ */
+
+struct ring_t *ring_new(struct ring_t *buf, size_t len) {
+  if(len < 3) {
+    return NULL; 
+  }
+
+  buf->buflen = len + 1;
+  buf->buffer = malloc(buf->buflen);
+
+  if(buf->buffer == NULL) {
+    return NULL;
+  }
+
+  buf->begin = buf->buffer;
+  buf->end = buf->buffer + len;
+  buf->writer = buf->buffer;
+  buf->reader = buf->buffer;
+  return buf;
+}
+
+/*
+ * ring_write
+ * write data into the buffer
+ *
+ * parameters:
+ *   struct ring_t *buf - ring object (provided by user)
+ *   char *str - string to write to the buffer
+ *   size_t orig_len - length of the string to write
+ *
+ * returns the number of characters left to write
+ */
+
+size_t ring_write(struct ring_t *buf, char *str, size_t orig_len) {
+  size_t len = orig_len;
+
+  while(len > 0) {
+    if(buf->writer == buf->end && buf->reader == buf->begin) {
+      break;
+    } else if(buf->writer == buf->end + 1) {
+      buf->writer = buf->begin;
+    }
+
+    if(buf->writer == buf->reader - 1) {
+      break;
+    }
+
+    *buf->writer = *str;
+    --len, ++str, ++buf->writer;
+  }
+
+  return len;
+}
+
+/*
+ * ring_read
+ * read data from the buffer
+ *
+ * parameters:
+ *   struct ring_t *buf - ring object (provided by user)
+ *   size_t *len - length of the string to read (modified to the number of characters read)
+ *
+ * returns the number of characters left to read
+ */
+
+char *ring_read(struct ring_t *buf, size_t *len) {
+  char *str = malloc(*len);
+  size_t index = 0;
+
+  if(str == NULL) {
+    return NULL;
+  }
+
+  while(index < *len && buf->reader != buf->writer) {
+    str[index] = *buf->reader;
+    ++index, ++buf->reader;
+
+    if(buf->reader == buf->end + 1) {
+      buf->reader = buf->begin;
+    }
+  }
+
+  if(index == 0) {
+    *len = 0;
+    return NULL;
+  } else {
+    *len -= index;
+    return str;
+  }
+}
+
+/*
+ * ring_readln
+ * read a line of data from the buffer
+ *
+ * parameters:
+ *   struct ring_t *buf - ring object (provided by user)
+ *   size_t *len - length of the line read
+ *
+ * returns the retreived line
+ */
+
+char *ring_readln(struct ring_t *buf, size_t *len) {
+  *len = 0;
+  char *index = buf->reader;
+
+  while(*index != '\n' && index != buf->writer) {
+    ++index, ++(*len);
+
+    if(index == buf->end + 1) {
+      index = buf->begin;
+    }
+  }
+
+  if(*index != '\n') {
+    *len = 0;
+    return NULL;
+  } else {
+    size_t length = *len + 1;
+    char *str = ring_read(buf, &length);
+
+    if(str != NULL) {
+      str[*len] = '\0';
+    }
+
+    return str;
+  }
+}
+
+/*
+ * ring_del
+ * delete a ring buffer object
+ *
+ * parameters:
+ *   struct ring_t *buf - ring object (provided by user)
+ *
+ * returns nothing
+ */
+
+void ring_del(struct ring_t *buf) {
+  buf->buflen = 0;
+  buf->begin = NULL;
+  buf->end = NULL;
+  buf->writer = NULL;
+  buf->reader = NULL;
+  free(buf->buffer);
+}