SDK for PHP V3

The address must be a valid textual IPv6 address without brackets and without a zone identifier, such as the inside of an IP-literal accepted by isValidHost(). Canonicalization lowercases the hexadecimal fields, suppresses leading zeros, and collapses the longest run of two or more zero fields (the leftmost on a tie) with ::. Embedded dotted-decimal notation follows the rendering policy of BIND-derived inet_ntop() implementations and curl: exactly the IPv4-mapped (::ffff:0:0/96) and deprecated IPv4-compatible (::/96) layouts use it, while other embedded-IPv4 forms, including translated (NAT64) well-known prefixes such as 64:ff9b::/96 (RFC 6052), serialize in pure hexadecimal fields.

Validation is strict and platform-independent: the address is checked against the RFC 3986 IPv6address grammar with PHP's FILTER_VALIDATE_IP filter and parsed in pure PHP, so spellings that only some platform parsers accept, such as the zero-padded dotted octets in ::ffff:192.168.001.001, are rejected everywhere.

Per RFC 3986 the host is IP-literal / IPv4address / reg-name. An empty host is accepted, since the authority (and thus the host) may be empty. Bracketed values are validated as IPv6 / IPvFuture literals; any other value is rejected if it contains control characters, whitespace, an authority or path delimiter (/ ? # @ \), an embedded colon denoting a port, a malformed percent-sequence, or a percent-encoded octet that decodes to one of those rejected bytes, to a bracket, or to % itself.

RFC 3986 defines the port as *DIGIT, which also permits an empty port and has no upper bound. This applies the stricter policy used throughout the library instead: the value must be a non-empty run of digits (leading zeros are accepted and normalized) that resolves to 0-65535.

Per RFC 3986 a scheme must start with a letter, followed by letters, digits, +, -, or .. The empty string is also accepted, since a URI reference may omit the scheme.