URI Regular Expression

uri_reference_regex.h

/**
 * Regex for validating a URI or URI Reference as defined in RFC3986.
 *
 * A URI Reference is a URI without the scheme part. They are otherwise the
 * same except that the first segment of a relative path of a URI reference
 * can't contain a ':'.
 *
 * This syntax does not have IPv6 address support and does not include the IPv4
 * rule because IPv4 addresses happens to be a subset of registered names.
 * Although the final regex can be made a little bit more compact the intent is
 * to follow the rules as closely as possible for readability and not introduce
 * any new rules.
 */
#define URI           SCHEME ":" HIER_PART "(\\?" QUERY ")?(#" FRAGMENT ")?"
#define HIER_PART     "(//" AUTHORITY PATH_ABEMPTY "|" PATH_ABSOLUTE "|" PATH_ROOTLESS "|" PATH_EMPTY ")"
#define URI_REFERENCE URI "|" RELATIVE_REF
#define RELATIVE_REF  RELATIVE_PART "(\\?" QUERY ")?(#" FRAGMENT ")?"
#define RELATIVE_PART "(//" AUTHORITY PATH_ABEMPTY "|" PATH_ABSOLUTE "|" PATH_NOSCHEME "|" PATH_EMPTY ")"
#define SCHEME        "[A-Za-z][A-Za-z0-9+.-]*"
#define AUTHORITY     "(" USERINFO "@)?" HOST "(:" PORT ")?"
#define USERINFO      "(" UNRESERVED "|" PCT_ENCODED "|" SUB_DELIMS "|:)*"
#define HOST          "(" UNRESERVED "|" PCT_ENCODED "|" SUB_DELIMS ")*"
#define PORT          "[0-9]*"
#define PATH_ABEMPTY  "(/" SEGMENT ")*"
#define PATH_ABSOLUTE "/(" SEGMENT_NZ "(/" SEGMENT ")*)?"
#define PATH_NOSCHEME SEGMENT_NZ_NC "(/" SEGMENT ")*"
#define PATH_ROOTLESS SEGMENT_NZ "(/" SEGMENT ")*"
#define PATH_EMPTY    "()"
#define SEGMENT       PCHAR "*"
#define SEGMENT_NZ    PCHAR "+"
#define SEGMENT_NZ_NC "(" UNRESERVED "|" PCT_ENCODED "|" SUB_DELIMS "|@)+"
#define PCHAR         "(" UNRESERVED "|" PCT_ENCODED "|" SUB_DELIMS "|[:@])"
#define QUERY         "(" PCHAR "|[/?])*"
#define FRAGMENT      "(" PCHAR "|[/?])*"
#define PCT_ENCODED   "%[0-9A-Fa-f]{2}"
#define UNRESERVED    "[A-Za-z0-9._~-]"
#define SUB_DELIMS    "[!$&'()*+,;=]"

uri_regex.h

/**
 * Syntax for a URI as defined in RFC3986.
 *
 * This syntax does not have IPv6 address support and does not include the IPv4
 * rule because IPv4 addresses happens to be a subset of registered names.
 */
#define URI SCHEME ":" HIER_PART "(?:\\?" QUERY ")?(?:#" FRAGMENT ")?"
#define HIER_PART "(?://" AUTHORITY PATH_ABEMPTY "|" PATH_ABSOLUTE "|" PATH_ROOTLESS "|" PATH_EMPTY ")"
#define SCHEME "(?<scheme>[[:alpha:]][[:alnum:]+.-]*)"
#define AUTHORITY "(?<authority>(?:" USERINFO "@)?" HOST "(?::" PORT ")?)"
#define USERINFO "(?<userinfo>(?:" UNRESERVED "|" PCT_ENCODED "|" SUB_DELIMS "|:)*)"
#define HOST "(?<host>(?:" UNRESERVED "|" PCT_ENCODED "|" SUB_DELIMS ")*)"
#define PORT "(?<port>[0-9]*)"
#define PATH_ABEMPTY "(?<path>(?:/" SEGMENT ")*)"
#define PATH_ABSOLUTE "(?<path>/(?:" SEGMENT_NZ "(?:/" SEGMENT ")*)?)"
#define PATH_ROOTLESS "(?<path>" SEGMENT_NZ "(?:/" SEGMENT ")*)"
#define PATH_EMPTY "(?<path>)"
#define SEGMENT PCHAR "*"
#define SEGMENT_NZ PCHAR "+"
#define PCHAR "(?:" UNRESERVED "|" PCT_ENCODED "|" SUB_DELIMS "|[:@])"
#define QUERY "(?<query>(?:" PCHAR "|[/?])*)"
#define FRAGMENT "(?<fragment>(?:" PCHAR "|[/?])*)"
#define PCT_ENCODED "%[[:xdigit:]]{2}"
#define UNRESERVED "[[:alnum:]._~-]"
#define SUB_DELIMS "[!$&'()*+,;=]"

Evaluated URI reference:
[A-Za-z][A-Za-z0-9+.-]*:(//(([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|:)*@)?([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=])*(:[0-9]*)?(/([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|[:@])*)*|/(([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|[:@])+(/([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|[:@])*)*)?|([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|[:@])+(/([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|[:@])*)*|())(\?(([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|[:@])|[/?])*)?(#(([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|[:@])|[/?])*)?|(//(([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|:)*@)?([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=])*(:[0-9]*)?(/([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|[:@])*)*|/(([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|[:@])+(/([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|[:@])*)*)?|([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|@)+(/([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|[:@])*)*|())(\?(([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|[:@])|[/?])*)?(#(([A-Za-z0-9._~-]|%[0-9A-Fa-f]{2}|[!$&'()*+,;=]|[:@])|[/?])*)?

Visualised:
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