Consolidate all convert_* functions into libi3.

Some minor fixes along the way as well. Very minor stuff, unlikely
to ever be visible to the user.

libi3/ucs2_conversion.c

@@ -0,0 +1,103 @@
+/*
+ * vim:ts=4:sw=4:expandtab
+ *
+ * i3 - an improved dynamic tiling window manager
+ * © 2009-2011 Michael Stapelberg and contributors (see also: LICENSE)
+ *
+ */
+#include <err.h>
+#include <errno.h>
+#include <iconv.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "libi3.h"
+
+static iconv_t utf8_conversion_descriptor = (iconv_t)-1;
+static iconv_t ucs2_conversion_descriptor = (iconv_t)-1;
+
+/*
+ * Converts the given string to UTF-8 from UCS-2 big endian. The return value
+ * must be freed after use.
+ *
+ */
+char *convert_ucs2_to_utf8(xcb_char2b_t *text, size_t num_glyphs) {
+    /* Allocate the output buffer (UTF-8 is at most 4 bytes per glyph) */
+    size_t buffer_size = num_glyphs * 4 * sizeof(char) + 1;
+    char *buffer = scalloc(buffer_size * sizeof(char));
+
+    /* We need to use an additional pointer, because iconv() modifies it */
+    char *output = buffer;
+    size_t output_size = buffer_size - 1;
+
+    if (utf8_conversion_descriptor == (iconv_t)-1) {
+        /* Get a new conversion descriptor */
+        utf8_conversion_descriptor = iconv_open("UTF-8", "UCS-2BE");
+        if (utf8_conversion_descriptor == (iconv_t)-1)
+            err(EXIT_FAILURE, "Error opening the conversion context");
+    }
+    else {
+        /* Reset the existing conversion descriptor */
+        iconv(utf8_conversion_descriptor, NULL, NULL, NULL, NULL);
+    }
+
+    /* Do the conversion */
+    size_t input_len = num_glyphs * sizeof(xcb_char2b_t);
+    size_t rc = iconv(utf8_conversion_descriptor, (char**)&text,
+            &input_len, &output, &output_size);
+    if (rc == (size_t)-1) {
+        perror("Converting to UTF-8 failed");
+        free(buffer);
+        return NULL;
+    }
+
+    return buffer;
+}
+
+/*
+ * Converts the given string to UCS-2 big endian for use with
+ * xcb_image_text_16(). The amount of real glyphs is stored in real_strlen,
+ * a buffer containing the UCS-2 encoded string (16 bit per glyph) is
+ * returned. It has to be freed when done.
+ *
+ */
+xcb_char2b_t *convert_utf8_to_ucs2(char *input, int *real_strlen) {
+    /* Calculate the input buffer size (UTF-8 is strlen-safe) */
+    size_t input_size = strlen(input);
+
+    /* Calculate the output buffer size and allocate the buffer */
+    size_t buffer_size = input_size * sizeof(xcb_char2b_t);
+    xcb_char2b_t *buffer = smalloc(buffer_size);
+
+    /* We need to use an additional pointer, because iconv() modifies it */
+    size_t output_size = buffer_size;
+    xcb_char2b_t *output = buffer;
+
+    if (ucs2_conversion_descriptor == (iconv_t)-1) {
+        /* Get a new conversion descriptor */
+        ucs2_conversion_descriptor = iconv_open("UCS-2BE", "UTF-8");
+        if (ucs2_conversion_descriptor == (iconv_t)-1)
+            err(EXIT_FAILURE, "Error opening the conversion context");
+    }
+    else {
+        /* Reset the existing conversion descriptor */
+        iconv(ucs2_conversion_descriptor, NULL, NULL, NULL, NULL);
+    }
+
+    /* Do the conversion */
+    size_t rc = iconv(ucs2_conversion_descriptor, (char**)&input,
+            &input_size, (char**)&output, &output_size);
+    if (rc == (size_t)-1) {
+        perror("Converting to UCS-2 failed");
+        free(buffer);
+        if (real_strlen != NULL)
+            *real_strlen = 0;
+        return NULL;
+    }
+
+    /* Return the resulting string's length */
+    if (real_strlen != NULL)
+        *real_strlen = (buffer_size - output_size) / sizeof(xcb_char2b_t);
+
+    return buffer;
+}