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1.0 URI Filenames In SQLite

Beginning with version 3.7.7, the SQLite database file argument to the sqlite3_open(), sqlite3_open16(), and sqlite3_open_v2() interfaces and to the ATTACH command can be specified either as an ordinary filename or as a Uniform Resource Identifier or URI. The advantage of using a URI filename is that query parameters on the URI can be used to control details of the newly created database connection. For example, an alternative VFS can be specified using a "vfs=" query parameter. Or the database can be opened read-only by using "mode=ro" as a query parameter.

2.0 Backwards Compatibility

In order to maintain full backwards compatibility for legacy applications, the URI filename capability is disabled by default. In order for URI filenames to work, one or more of the following must be true:

The SQLite library is compiled with the SQLITE_USE_URI compile-time option.
The sqlite3_config(SQLITE_CONFIG_URI, 1); configuration option is set at application start-time.
The SQLITE_OPEN_URI bit is OR-ed in with the set bits passed in as the 3rd parameter to the sqlite3_open_v2() interface.

If URI filenames are recognized when the database connection is originally opened, then URI filenames will also be recognized on ATTACH statements. Similarly, if URI filenames are not recognized when the database connection is first opened, they will not be recognized by ATTACH.

Since SQLite always interprets any filename that does not begins with "file:" as an ordinary filename regardless of the URI setting, and because it is very unusual to have an actual file begin with "file:", it is safe for most applications to enable URI processing even if URI filenames are not currently being used.

3.0 URI Format

According to RFC 3986, a URI consists of a scheme, an authority, a path, a query string, and a fragment. The scheme is always required. One of either the authority or the path is also always required. The query string and fragment are optional.

SQLite uses the "file:" URI syntax to identify database files. SQLite strives to interpret file: URIs in exactly the same way as popular web-browsers such as Firefox, Chrome, Safari, Internet Explorer, and Opera, and command-line programs such as Windows "start" and the Mac OS-X "open" command. A succinct summary of the URI parsing rules follows:

The scheme of the URI must be "file:". Any other scheme results in the input being treated as an ordinary filename.
The authority may be omitted, may be blank, or may be "localhost". Any other authority results in an error.
The path is optional if the authority is present. If the authority is omitted then the path is required.
The query string is optional. If the query string is present, then all query parameters are passed through into the xOpen method of the underlying VFS.
The fragment is optional. If present, it is ignored.

Zero or more escape sequences of the form "%HH" (where H represents any hexadecimal digit) can occur in the path, query string, or fragment.

A filename that is not a well-formed URI is interpreted as an ordinary filename.

URIs are processed as UTF8 text. The filename argument sqlite3_open16() is converted from UTF16 native byte order into UTF8 prior to processing.

3.1 The URI Path

The path component of the URI specifies the disk file that is the SQLite database to be opened. If the path component is omitted, then the database is stored in a temporary file that will be automatically deleted when the database connection closes. If the authority section is present, then the path is always an absolute pathname. If the authority section is omitted, then the path is an absolute pathname if it begins with the "/" character (ASCII code 0x2f) and is a relative pathname otherwise. On windows, if the absolute path begins with "/X:/" where X is any single ASCII alphabetic character ("a" through "z" or "A" through "Z") then the "X:" is understood to be the drive letter of the volume containing the file, not the toplevel directory.

An ordinary filename can usually be converted into an equivalent URI by the steps shown below. The one exception is that a relative windows pathname with a drive letter cannot be converted directly into a URI; it must be changed into an absolute pathname first.

Convert all "?" characters into "%3f".
Convert all "#" characters into "%23".
On windows only, convert all "\" characters into "/".
Convert all sequences of two or more "/" characters into a single "/" character.
On windows only, if the filename begins with a drive letter, prepend a single "/" character.
Prepend the "file:" scheme.

3.2 Query String

A URI filename can optionally be followed by a query string. The query string consists of text following the first "?" character but excluding the optional fragment that begins with with "#". The query string is divided into key/value pairs. We usually refer to these key/value pairs as "query parameters". Key/value pairs are separated by a single "&" character. The key comes first and is separated from the value by a single "=" character. Both key and value may contain %HH escape sequences.

The text of query parameters is appended to the filename argument of the xOpen method of the VFS. Any %HH escape sequences in the query parameters are resolved prior to being appended to the xOpen filename. A single zero-byte separates the xOpen filename argument from the key of the first query parameters, each key and value, and each subsequent key from the prior value. The list of query parameters parameters appended to the xOpen filename is terminated by a single zero-length key. Note that the value of a query parameter can be an empty string.

3.3 Recognized Query Parameters

Some query parameters are interpreted by the SQLite core and used to modify the characteristics of the new connection. All query parameters are always passed through into the xOpen method of the VFS even if they are previously read and interpreted by the SQLite core.

The following query parameters are recognized by SQLite as of version 3.7.10. Other query parameters might be added to this set in future releases.