add hex_decode

docs/crypto.md

@@ -22,3 +22,22 @@ in case you need to know the size of the decoded data, otherwise you can just pa
 ```c
 unsigned char *b64_decode(const char *s, size_t sz, size_t *decode_sz);
 ```
+
+### hex_decode
+
+Decodes a string of characters representing hexadecimal bytes into an array of `unsigned char`.
+For example, converts `"DEADBEEF"` into `[0xDE, 0xAD, 0xBE, 0xEF]`.
+
+```c
+unsigned char *hex_decode(const char *orig, size_t *sz);
+
+// Example
+s = hex_decode("DEADBEEF", &s_sz);
+unsigned char h[4] = {
+    0xDE, 0xAD, 0xBE, 0xEF
+};
+for (size_t i = 0; i < 4; ++i) {
+    assert(s[i] == h[i]);
+}
+free(s);
+```

include/lfcrypto.h

@@ -3,7 +3,8 @@
 
 #include <stddef.h>
 
-char *b64_encode(const unsigned char *s, size_t sz);
+unsigned char *b64_encode(const unsigned char *s, size_t sz);
 unsigned char *b64_decode(const char *s, size_t sz, size_t *decode_sz);
+unsigned char *hex_decode(const char *orig, size_t *sz);
 
 #endif // LIBFLINT_CRYPTO_H

src/crypto.c

@@ -1,6 +1,7 @@
 #include <string.h>
 #include <stdlib.h>
 #include <ctype.h>
+#include <stdio.h>
 
 #include "lfcrypto.h"
 
@@ -18,7 +19,7 @@ static const char b64_table[] = {
 };
 
 typedef struct {
-    char *ptr;
+    unsigned char *ptr;
     int count;
 } b64_buf;
 
@@ -44,7 +45,7 @@ static int resize_b64_buf(b64_buf *b, size_t sz) {
     return 0;
 }
 
-char *b64_encode(const unsigned char *s, size_t sz) {
+unsigned char *b64_encode(const unsigned char *s, size_t sz) {
     int i = 0;
     b64_buf encbuf;
     size_t size = 0;
@@ -198,5 +199,28 @@ unsigned char *b64_decode(const char *s, size_t sz, size_t *decode_sz) {
         *decode_sz = size;
     }
 
-    return (unsigned char*)decbuf.ptr;
+    return decbuf.ptr;
+}
+
+unsigned char *hex_decode(const char *orig, size_t *sz) {
+    size_t buf_sz = strlen(orig) + 1;
+    if (strlen(orig) % 2 != 0) {
+        buf_sz += 1;
+    }
+
+    char *buf = malloc(sizeof(char) * buf_sz);
+    strcpy(buf, orig);
+    buf[buf_sz - 1] = '\0';
+
+    *sz = buf_sz / 2;
+    unsigned char *hex = malloc(sizeof(unsigned char) * *sz);
+    const char *pos = buf;
+
+    for (size_t i = 0; i < *sz; ++i) {
+        sscanf(pos, "%2hhx", &hex[i]);
+        pos += 2;
+    }
+
+    free(buf);
+    return hex;
 }

tests/tests.c

@@ -311,7 +311,7 @@ void test_string() {
 
 void test_crypto() {
     char *in = "BUTT";
-    char *s = b64_encode(in, strlen(in));
+    unsigned char *s = b64_encode(in, strlen(in));
     assert(strcmp(s, "QlVUVA==") == 0);
     free(s);
 
@@ -326,6 +326,15 @@ void test_crypto() {
     assert(strcmp(s, "a longer base64 test, apparently") == 0);
     assert(strlen(s) == s_sz);
     free(s);
+
+    s = hex_decode("DEADBEEF", &s_sz);
+    unsigned char h[4] = {
+            0xDE, 0xAD, 0xBE, 0xEF
+    };
+    for (size_t i = 0; i < 4; ++i) {
+        assert(s[i] == h[i]);
+    }
+    free(s);
 }
 
 #if defined(__APPLE__) || defined(__MACH__)