misc: Introduce ssh_log_hexdump()

The introduced internal function is intended to be a replacement for the
deprecated function ssh_print_hexa().

Signed-off-by: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/misc.h

@@ -83,4 +83,5 @@ int ssh_match_group(const char *group, const char *object);
 
 void uint64_inc(unsigned char *counter);
 
+void ssh_log_hexdump(const char *descr, const unsigned char *what, size_t len);
 #endif /* MISC_H_ */

src/misc.c

@@ -389,6 +389,193 @@ void ssh_print_hexa(const char *descr, const unsigned char *what, size_t len) {
     free(hexa);
 }
 
+/**
+ * @brief Log the content of a buffer in hexadecimal format, similar to the
+ * output of 'hexdump -C' command.
+ *
+ * The first logged line is the given description followed by the length.
+ * Then the content of the buffer is logged 16 bytes per line in the following
+ * format:
+ *
+ * (offset) (first 8 bytes) (last 8 bytes) (the 16 bytes as ASCII char values)
+ *
+ * The output for a 16 bytes array containing values from 0x00 to 0x0f would be:
+ *
+ * "Example (16 bytes):"
+ * "  00000000  00 01 02 03 04 05 06 07  08 09 0a 0b 0c 0d 0e 0f  ................"
+ *
+ * The value for each byte as corresponding ASCII character is printed at the
+ * end if the value is printable. Otherwise it is replace with '.'.
+ *
+ * @param[in] descr A description for the content to be logged
+ * @param[in] what  The buffer to be logged
+ * @param[in] len   The length of the buffer given in what
+ *
+ * @note If a too long description is provided (which would result in a first
+ * line longer than 80 bytes), the function will fail.
+ */
+void ssh_log_hexdump(const char *descr, const unsigned char *what, size_t len)
+{
+    size_t i;
+    char ascii[17];
+    const unsigned char *pc = NULL;
+    size_t count = 0;
+    ssize_t printed = 0;
+
+    /* The required buffer size is calculated from:
+     *
+     *  2 bytes for spaces at the beginning
+     *  8 bytes for the offset
+     *  2 bytes for spaces
+     * 24 bytes to print the first 8 bytes + spaces
+     *  1 byte for an extra space
+     * 24 bytes to print next 8 bytes + spaces
+     *  2 bytes for extra spaces
+     * 16 bytes for the content as ASCII characters at the end
+     *  1 byte for the ending '\0'
+     *
+     * Resulting in 80 bytes.
+     *
+     * Except for the first line (description + size), all lines have fixed
+     * length. If a too long description is used, the function will fail.
+     * */
+    char buffer[80];
+
+    /* Print description */
+    if (descr != NULL) {
+        printed = snprintf(buffer, sizeof(buffer), "%s ", descr);
+        if (printed < 0) {
+            goto error;
+        }
+        count += printed;
+    } else {
+        printed = snprintf(buffer, sizeof(buffer), "(NULL description) ");
+        if (printed < 0) {
+            goto error;
+        }
+        count += printed;
+    }
+
+    if (len == 0) {
+        printed = snprintf(buffer + count, sizeof(buffer) - count,
+                           "(zero length):");
+        if (printed < 0) {
+            goto error;
+        }
+        SSH_LOG(SSH_LOG_DEBUG, "%s", buffer);
+        return;
+    } else {
+        printed = snprintf(buffer + count, sizeof(buffer) - count,
+                           "(%zu bytes):", len);
+        if (printed < 0) {
+            goto error;
+        }
+        count += printed;
+    }
+
+    if (what == NULL) {
+        printed = snprintf(buffer + count, sizeof(buffer) - count,
+                           "(NULL)");
+        if (printed < 0) {
+            goto error;
+        }
+        SSH_LOG(SSH_LOG_DEBUG, "%s", buffer);
+        return;
+    }
+
+    SSH_LOG(SSH_LOG_DEBUG, "%s", buffer);
+
+    /* Reset state */
+    count = 0;
+    pc = what;
+
+    for (i = 0; i < len; i++) {
+        /* Add one space after printing 8 bytes */
+        if ((i % 8) == 0) {
+            if (i != 0) {
+                printed = snprintf(buffer + count, sizeof(buffer) - count, " ");
+                if (printed < 0) {
+                    goto error;
+                }
+                count += printed;
+            }
+        }
+
+        /* Log previous line and reset state for new line */
+        if ((i % 16) == 0) {
+            if (i != 0) {
+                printed = snprintf(buffer + count, sizeof(buffer) - count,
+                                   "  %s", ascii);
+                if (printed < 0) {
+                    goto error;
+                }
+                SSH_LOG(SSH_LOG_DEBUG, "%s", buffer);
+                count = 0;
+            }
+
+            /* Start a new line with the offset */
+            printed = snprintf(buffer, sizeof(buffer),
+                               "  %08zx ", i);
+            if (printed < 0) {
+                goto error;
+            }
+            count += printed;
+        }
+
+        /* Print the current byte hexadecimal representation */
+        printed = snprintf(buffer + count, sizeof(buffer) - count,
+                           " %02x", pc[i]);
+        if (printed < 0) {
+            goto error;
+        }
+        count += printed;
+
+        /* If printable, store the ASCII character */
+        if (isprint(pc[i])) {
+            ascii[i % 16] = pc[i];
+        } else {
+            ascii[i % 16] = '.';
+        }
+        ascii[(i % 16) + 1] = '\0';
+    }
+
+    /* Add padding if not exactly 16 characters */
+    while ((i % 16) != 0) {
+        /* Add one space after printing 8 bytes */
+        if ((i % 8) == 0) {
+            if (i != 0) {
+                printed = snprintf(buffer + count, sizeof(buffer) - count, " ");
+                if (printed < 0) {
+                    goto error;
+                }
+                count += printed;
+            }
+        }
+
+        printed = snprintf(buffer + count, sizeof(buffer) - count, "   ");
+        if (printed < 0) {
+            goto error;
+        }
+        count += printed;
+        i++;
+    }
+
+    /* Print the last printable part */
+    printed = snprintf(buffer + count, sizeof(buffer) - count,
+                       "   %s", ascii);
+    if (printed < 0) {
+        goto error;
+    }
+
+    SSH_LOG(SSH_LOG_DEBUG, "%s", buffer);
+
+    return;
+
+error:
+    SSH_LOG(SSH_LOG_WARN, "Could not print to buffer");
+    return;
+}
+
 /**
  * @brief Check if libssh is the required version or get the version
  * string.