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cha-protocols(7) Protocol support in Chawan cha-protocols(7) Protocols Chawan supports downloading resources from various protocols: HTTP, FTP, SFTP, Gopher, Gemini, Spartan, and Finger. Details on these pro- tocols, and information on how users can add support to their preferred protocols is outlined in this document. You can find network adapters in the source distribution's adapter/pro- tocol directory. For protocol-specific file formats (like gemtext or gopher directories) you will also find an appropriate HTML converter in adapter/format. HTTP HTTP/s support is implemented in Nim. It supports HTTP/1.1 with arbi- trary headers and POST data, is able to use passed userinfo data, and returns all headers and response body it receives without exception. Deflate decompression with gzip and zlib headers is supported. (Ac- cept-Encoding: gzip, deflate.) This is based on a modified version of the public domain tinfl.h decompressor by Rich Geldreich. Brotli decompression (Accept-Encoding: br) is supported using the de- coder provided by the reference implementation. The bonus directory contains two alternative HTTP clients: • curlhttp; this is the old HTTP client based on libcurl. It can be built using curl-impersonate; see README.md in the bonus/ directory for details. • libfetch-http: based on FreeBSD libfetch. It is mostly a proof of concept, as FreeBSD libfetch HTTP support is very limited; in partic- ular, it does not support arbitrary HTTP headers, so e.g. cookies will not work. FTP Chawan supports FTP passive mode browsing and downloads. For directory listings, it assumes UNIX output style, and will probably break horribly on receiving anything else. Otherwise, the directory listing view is identical to the file:// directory listing. SFTP The sftp adapter (adapter/protocol/sftp.nim) wraps libssh2. It works for me, but YMMV. Note that if an IdentityFile declaration is found in your ssh config, then it will prompt for the identity file password, but there is no way to tell whether it is really asking for that (or just normal password auth). Also, settings covered by the Match field are ignored. Gopher Chawan supports the Gopher protocol through the gopher CGI program. Gopher directories are passed as the text/gopher type, and gopher2html takes care of converting this to HTML. Gopher selector types are converted to MIME types when possible; note however, that this is very limited, as most of them (like s sound, or I image) cannot be unambiguously converted without some other sniffing method. Chawan will fall back to extension-based detection in these cases, and in the worst case may end up with application/octet-stream. Gemini Chawan's Gemini adapter has been rewritten as a Nim program. It still requires OpenSSL to work. A limitation that remains is that the Gemini adapter does not support sites that require private key authentication. gmi2html is its companion program to convert the text/gemini file for- mat to HTML. Finger Finger is supported through the finger shell script. It is implemented as a shell script because of the protocol's simplicity. For portability, finger uses Chawan's nc tool (a very limited netcat clone) to make requests. Spartan Spartan is a protocol similar to Gemini, but without TLS. It is sup- ported through the spartan shell script, and like Finger, it uses Chawan's nc to make requests. Spartan has the very strange property of extending gemtext with a pro- tocol-specific line type. This is sort of supported through a sed fil- ter for gemtext outputs in the CGI script (in other words, no modifica- tion to gmi2html was done to support this). Local schemes: file:, man: While these are not necessarily protocols, they are implemented simi- larly to the protocols listed above (and thus can also be replaced, if the user wishes; see below). file: loads a file from the local filesystem. In case of directories, it shows the directory listing like the FTP protocol does. man:, man-k: and man-l: are wrappers around the commands man, man -k and man -l. These look up man pages using /usr/bin/man and turn on-page references into links. A wrapper command mancha also exists; this has an interface similar to man. Note: this used to be based on w3mman2html.cgi, but it has been rewritten in Nim (and therefore no longer depends on Perl either). Internal schemes: cgi-bin:, stream:, cache:, data:, about: Five internal protocols exist: cgi-bin:, stream:, cache:, data: and about:. These are the basic building blocks for the implementation of every protocol mentioned above; for this reason, these can not be re- placed, and are implemented in the main browser binary. cgi-bin: executes a local CGI script. This scheme is used for the ac- tual implementation of the non-internal protocols mentioned above. Lo- cal CGI scripts can also be used to implement wrappers of other pro- grams inside Chawan (e.g. dictionaries). stream: is used for streams returned by external programs. It differs from cgi-bin: in that it does not cooperate with the external process, and that the loader does not keep track of where the stream originally comes from. Therefore it is suitable for reading in the output of mailcap entries, or for turning stdin into a URL. It is not possible to reload stream: URLs. To support rewinding and "view source", the output of stream:'s is stored in a cache file until the buffer is discarded. cache: is not something an end user would normally see; it's used for rewinding or re-interpreting streams already downloaded. Caching works differently than in most other browsers; files are deter- ministically loaded from the cache upon certain actions, and from the network upon others, but neither is used as a fallback to the other. data: decodes a data URL as defined in RFC 2397. This used to be a CGI module, but has been moved back into the loader process because these URLs can get so long that they no longer fit into the environment. about: is inside the loader to allow for an implementation of the down- load list panel. It should be turned into a CGI module once the loader gets RPC capabilities. The following about pages are available: about:chawan, about:blank, about:license, about:download. Custom protocols Chawan is protocol-agnostic. This means that the cha binary itself does not know much about the protocols listed above; instead, it loads these through a combination of local CGI, urimethodmap, and if conver- sion to HTML or plain text is necessary, mailcap (using x-htmloutput, x-ansioutput and copiousoutput). urimethodmap can also be used to override default handlers for the pro- tocols listed above. This is similar to how w3m allows you to override the default directory listing display, but much more powerful; this way, any library or program that can retrieve and output text through a certain protocol can be combined with Chawan. For example, consider the urimethodmap definition of cha-finger: finger: cgi-bin:cha-finger This commands Chawan to load the cha-finger CGI script, setting the $MAPPED_URI_* variables to the target URL's parts in the process. Then, cha-finger uses these passed parts to construct an appropriate curl command that will retrieve the specified finger: URL; it prints the header `Content-Type: text/plain' to the output, then an empty line, then the body of the retrieved resource. If an error is encoun- tered, it prints a Cha-Control header with an error code and a specific error message instead. Adding a new protocol Here we will add a protocol called "cowsay", so that the URL cowsay:text prints the output of cowsay text after a second of waiting. mkdir -p ~/.chawan/cgi-bin, and create a CGI script in ~/.chawan/cgi-bin/cowsay.cgi: #!/bin/sh # We are going to wait a second from now, but want Chawan to show # "Downloading..." instead of "Connecting...". So signal to the browser that the # connection has succeeded. printf 'Cha-Control: Connected\n' sleep 1 # sleep # Status is a special header that signals the equivalent HTTP status code. printf 'Status: 200' # HTTP OK # Tell the browser that no more control headers are to be expected. # This is useful when you want to send remotely received headers; then, it would # be an attack vector to simply send the headers without ControlDone, as nothing # stops the website from sending a Cha-Control header. With ControlDone sent, # even Cha-Control headers will be interpreted as regular headers. printf 'Cha-Control: ControlDone\n' # As in HTTP, you must send an empty line before the body. printf '\n' # Now, print the body. We take the path passed to the URL; urimethodmap # sets this as MAPPED_URI_PATH. This is URI-encoded, so we also run the urldec # utility on it. cowsay "$(printf '%s\n' "$MAPPED_URI_PATH" | "$CHA_LIBEXEC_DIR"/urldec)" Now, create a ".urimethodmap" file in your $HOME directory. Then, enter into it the following: cowsay: /cgi-bin/cowsay.cgi Now try cha cowsay:Hello,%20world.. If you did everything correctly, it should wait one second, then print a cow saying "Hello, world.". See also cha(1), cha-localcgi(5), cha-urimethodmap(5), cha-mailcap(5) cha-protocols(7)
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