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| | If you have problems with other clients or servers, please upgrade (or ask the server to upgrade) to FTP software capable of UTF-8 or refrain from using foreign characters. Anything else is in violation of the FTP specifications and will only work if you manually ensure that the server and client use the same character encoding (which may not even be possible). | | If you have problems with other clients or servers, please upgrade (or ask the server to upgrade) to FTP software capable of UTF-8 or refrain from using foreign characters. Anything else is in violation of the FTP specifications and will only work if you manually ensure that the server and client use the same character encoding (which may not even be possible). |
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| − | == Technical details ==
| + | I've been looknig for a post like this for an age |
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| − | The FTP protocol is specified in [http://filezilla-project.org/specs/rfc0959.txt <nowiki>RFC 959</nowiki>], which was published in 1985. The FTP protocol is designed on top of the original Telnet protocol, which is specified in [http://filezilla-project.org/specs/rfc0854.txt <nowiki>RFC 854</nowiki>]. The relevant sections of the Telnet specification regarding FTP are those covering the Network Virtual Terminal (NVT).
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| − | According to [http://filezilla-project.org/specs/rfc0854.txt RFC 854], the NVT requires the use of (7-bit) ASCII as the character set. Use of any other character set requires explicit negotiation. This character set only contains 127 different characters: English letters and numbers, punctuation characters and a few control characters. Accented letters, umlauts or other scripts are not contained in the ASCII character set.
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| − | In order to support non-English characters, the FTP specifications were extended in 1999 in [http://filezilla-project.org/specs/rfc2640.txt <nowiki>RFC 2640</nowiki>]. This extension requires the use of UTF-8 as the character set. This character set is a strict superset of ASCII, every valid ASCII character is also the same character in UTF-8. The UTF-8 character set can display any valid Unicode character. That includes umlauts, accented letters and also different scripts.
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| − | This extension is fully backwards compatible with [http://filezilla-project.org/specs/rfc0959.txt <nowiki>RFC 959</nowiki>].
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| − | As long as you're using only English characters, it doesn't matter if the software you are using supports RFC 2640 or not. However, if you use non-English characters without using RFC 2640 compatible software, there will be problems--problems which are entirely self-made by not obeying the specifications.
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| − | === UTF8 feature negotiation ===
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| − | An [http://filezilla-project.org/specs/rfc2640.txt <nowiki>RFC 2640</nowiki>] compliant server ''must'' support the FEAT command and ''must'' include a line containing UTF8 in its response:
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| − | Command: FEAT
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| − | Response: 211-Features:
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| − | [...]
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| − | Response: UTF8
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| − | [...]
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| − | Response: 211 End
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| − | === Conflicting specification ===
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| − | There exists a long expired [http://tools.ietf.org/html/draft-ietf-ftpext-utf-8-option-00 IETF draft] that is in conflict with [http://filezilla-project.org/specs/rfc2640.txt <nowiki>RFC 2640</nowiki>]. This draft also requires the FEAT response to include UTF8, but in addition requires the client to send '''OPTS UTF-8 ON''' to enable UTF-8 support.
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| − | If an [http://filezilla-project.org/specs/rfc2640.txt <nowiki>RFC 2640</nowiki>] compliant client sends '''OPTS UTF-8 ON''', it has to use UTF-8 regardless whether '''OPTS UTF-8 ON''' succeeds or not.
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| − | [http://filezilla-project.org/specs/rfc2640.txt <nowiki>RFC 2640</nowiki>] compliant servers ''must not'' make UTF-8 dependent on '''OPTS UTF-8 ON'''.
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| − | === SFTP ===
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| − | The situation for SFTP is similar to the one for FTP. Current versions of the SFTP specifications (beginning with version 4) require filenames to be encoded as UTF-8.
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| − | However, the most commonly used SFTP protocol version is version 3 as implemented in OpenSSH. This version of the SFTP specifications does not require UTF-8. In fact it does not say anything about the encoding.
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| − | It is however reasonable to assume UTF-8 on those servers for the following reasons:
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| − | * The later protocol versions require UTF-8
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| − | * The SSH protocol, under which SFTP operates, already requires UTF-8
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| − | * Even in version 3 of the protocol, some parts of the protocol already use UTF-8
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| − | * The native character set on most modern Unix(-like) operating systems is UTF-8
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| − | In essence this means that everywhere where SFTP is available, the necessary infrastructure to use UTF-8 is in place.
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