url.h — Lightweight URL Parser

Introduction

url.h provides xUrl, a lightweight URL parser that decomposes a URL string into its RFC 3986 components: scheme, userinfo, host, port, path, query, and fragment. The parser makes a single internal copy of the input; all component fields are pointer+length pairs referencing this copy, so the caller may discard the original string immediately after parsing.

Design Philosophy

1. Single Copy, Zero Per-Field Allocation — xUrlParse() calls strdup() once. All output fields point into this copy, avoiding per-component heap allocations.

2. Pointer+Length Pairs — Fields use const char * + size_t pairs rather than NUL-terminated strings. This avoids mutating the internal copy and supports efficient substring access.

3. Scheme-Aware Default Ports — xUrlPort() returns well-known default ports (80 for http/ws, 443 for https/wss) when no explicit port is present, simplifying connection logic.

4. IPv6 Literal Support — The parser correctly handles bracketed IPv6 addresses ([::1]:8080), extracting the bare address without brackets.

Architecture

flowchart LR
    INPUT["Raw URL string"]
    PARSE["xUrlParse()"]
    COPY["strdup() internal copy"]
    FIELDS["Pointer+Length fields"]
    PORT["xUrlPort()"]
    FREE["xUrlFree()"]

    INPUT --> PARSE
    PARSE --> COPY
    COPY --> FIELDS
    FIELDS --> PORT
    FIELDS --> FREE

    style PARSE fill:#4a90d9,color:#fff
    style FREE fill:#e74c3c,color:#fff

Implementation Details

URL Format

scheme://[userinfo@]host[:port][/path][?query][#fragment]

Parsing Steps

flowchart TD
    START["Input: raw URL string"]
    SCHEME["Find '://' → extract scheme"]
    AUTH["Parse authority section"]
    USERINFO{"Contains '@'?"}
    UI_YES["Extract userinfo"]
    HOST{"Starts with '['?"}
    IPV6["Parse IPv6 bracket literal"]
    IPV4["Scan backwards for ':'"]
    PORT["Extract port (if present)"]
    PATH{"Starts with '/'?"}
    PATH_YES["Extract path"]
    QUERY{"Starts with '?'?"}
    QUERY_YES["Extract query"]
    FRAG{"Starts with '#'?"}
    FRAG_YES["Extract fragment"]
    DONE["Return xErrno_Ok"]

    START --> SCHEME --> AUTH
    AUTH --> USERINFO
    USERINFO -->|Yes| UI_YES --> HOST
    USERINFO -->|No| HOST
    HOST -->|Yes| IPV6 --> PORT
    HOST -->|No| IPV4 --> PORT
    PORT --> PATH
    PATH -->|Yes| PATH_YES --> QUERY
    PATH -->|No| QUERY
    QUERY -->|Yes| QUERY_YES --> FRAG
    QUERY -->|No| FRAG
    FRAG -->|Yes| FRAG_YES --> DONE
    FRAG -->|No| DONE

    style DONE fill:#50b86c,color:#fff

Memory Layout

xUrl struct (stack or heap):
┌──────────┬──────────────────────────────────┐
│  raw_    │→ strdup("https://host:443/path") │
│  scheme  │→ ───────┘                        │
│  host    │→ ──────────────┘                 │
│  port    │→ ───────────────────┘            │
│  path    │→ ────────────────────────┘       │
│  ...     │                                  │
└──────────┴──────────────────────────────────┘
All pointers reference the single raw_ copy.

Operations and Complexity

API Reference

Lifecycle

Query

xUrl Fields

Note: Optional fields have ptr=NULL, len=0 when absent. The raw_ field is internal — do not access it.

Usage Examples

Basic URL Parsing

#include <stdio.h>
#include <xnet/url.h>

int main(void) {
    xUrl url;
    xErrno err = xUrlParse("https://user:[email protected]:8443/ws/chat?token=abc#top", &url);
    if (err != xErrno_Ok) {
        fprintf(stderr, "parse failed\n");
        return 1;
    }

    printf("scheme:   %.*s\n", (int)url.scheme_len, url.scheme);
    printf("userinfo: %.*s\n", (int)url.userinfo_len, url.userinfo);
    printf("host:     %.*s\n", (int)url.host_len, url.host);
    printf("port:     %.*s (numeric: %u)\n", (int)url.port_len, url.port, xUrlPort(&url));
    printf("path:     %.*s\n", (int)url.path_len, url.path);
    printf("query:    %.*s\n", (int)url.query_len, url.query);
    printf("fragment: %.*s\n", (int)url.fragment_len, url.fragment);

    xUrlFree(&url);
    return 0;
}

Output:

scheme:   https
userinfo: user:pass
host:     example.com
port:     8443 (numeric: 8443)
path:     /ws/chat
query:    token=abc
fragment: top

IPv6 Address

xUrl url;
xUrlParse("http://[::1]:8080/test", &url);

printf("host: %.*s\n", (int)url.host_len, url.host);
// Output: host: ::1  (brackets stripped)

printf("port: %u\n", xUrlPort(&url));
// Output: port: 8080

xUrlFree(&url);

Default Port by Scheme

xUrl url;
xUrlParse("wss://echo.example.com/sock", &url);

// No explicit port in URL
printf("port field: %s\n", url.port ? "present" : "absent");
// Output: port field: absent

// xUrlPort() returns 443 for wss://
printf("effective port: %u\n", xUrlPort(&url));
// Output: effective port: 443

xUrlFree(&url);

Ownership Semantics

// xUrl owns its data — the original string can be freed
char *heap = strdup("ws://example.com:9090/ws");
xUrl url;
xUrlParse(heap, &url);
free(heap);  // safe: xUrl has its own copy

// url fields are still valid here
printf("host: %.*s\n", (int)url.host_len, url.host);

xUrlFree(&url);
// After free, all fields are zeroed (NULL)

Error Handling

On error, the xUrl struct is zeroed — no cleanup needed.

Best Practices

• Always check the return value of xUrlParse(). On error the struct is zeroed, so accessing fields is safe but yields empty values.
• Use xUrlPort() instead of parsing the port string yourself. It handles default ports and validates the numeric range (0–65535).
• Call xUrlFree() when done. Forgetting to free leaks the internal string copy.
• Don't cache field pointers past xUrlFree(). All pointers become invalid after the free call.