From c9533cb89bc9d209d48314c7d608090b3d6ab7b5 Mon Sep 17 00:00:00 2001 From: Vivien Kraus Date: Sun, 21 Feb 2021 01:44:01 +0100 Subject: First commit --- AUTHORS | 6 + COPYING | 3 + ChangeLog | 1 + Makefile.am | 44 ++++ NEWS | 7 + README | 7 + bootstrap | 7 + configure.ac | 13 ++ doc/fdl.texi | 505 ++++++++++++++++++++++++++++++++++++++++++ pre-inst-env.in | 15 ++ web-client-with-cache.org | 542 ++++++++++++++++++++++++++++++++++++++++++++++ 11 files changed, 1150 insertions(+) create mode 100644 AUTHORS create mode 100644 COPYING create mode 100644 ChangeLog create mode 100644 Makefile.am create mode 100644 NEWS create mode 100644 README create mode 100755 bootstrap create mode 100644 configure.ac create mode 100644 doc/fdl.texi create mode 100644 pre-inst-env.in create mode 100644 web-client-with-cache.org diff --git a/AUTHORS b/AUTHORS new file mode 100644 index 0000000..8dcea61 --- /dev/null +++ b/AUTHORS @@ -0,0 +1,6 @@ +-*- mode: org; coding: utf-8; -*- + +#+TITLE: Web-Client-With-Cache NEWS – authors +#+STARTUP: content hidestars + +- Vivien Kraus [[mailto:vivien@planete-kraus.eu]] \ No newline at end of file diff --git a/COPYING b/COPYING new file mode 100644 index 0000000..f658e91 --- /dev/null +++ b/COPYING @@ -0,0 +1,3 @@ +This project's license is GPL 3+. + +You can read the full license at https://www.gnu.org/licenses/gpl.html. diff --git a/ChangeLog b/ChangeLog new file mode 100644 index 0000000..76c33bf --- /dev/null +++ b/ChangeLog @@ -0,0 +1 @@ +For a complete log, please see the Git commit log at . diff --git a/Makefile.am b/Makefile.am new file mode 100644 index 0000000..70babd4 --- /dev/null +++ b/Makefile.am @@ -0,0 +1,44 @@ +DISTCHECK_CONFIGURE_FLAGS = CONFIG_SHELL=$(CONFIG_SHELL) SHELL=$(SHELL) +ACLOCAL_AMFLAGS = -I m4 +nodist_noinst_SCRIPTS = pre-inst-env + +EXTRA_DIST = web-client-with-cache.org + +moddir = $(prefix)/share/guile/site/$(GUILE_EFFECTIVE_VERSION) +godir = $(libdir)/guile/$(GUILE_EFFECTIVE_VERSION)/site-ccache + +webmoddir = $(moddir)/web +webgodir = $(godir)/web +clientwebmoddir = $(webmoddir)/client +clientwebgodir = $(webgodir)/client + +dist_clientwebmod_DATA = $(srcdir)/web/client/with-cache.scm +clientwebgo_DATA = web/client/with-cache.go + +install_go_targets = install-clientwebgoDATA +install_mod_targets = install-dist_clientwebmodDATA + +CLEANFILES = $(clientwebgo_DATA) + +SUFFIXES = .scm .go +.scm.go: + $(AM_V_GEN) $(top_builddir)/pre-inst-env $(GUILD) compile $(GUILE_WARNINGS) $(GUILD_OPTIONS) -o "$@-t" "$<" + @mv "$@-t" "$@" + +$(install_go_targets): $(install_mod_targets) + +$(srcdir)/web/client/with-cache.scm: web-client-with-cache.org + $(AM_V_GEN) $(EMACS) --batch \ + --file $(srcdir)/$< \ + --eval "(setq org-confirm-babel-evaluate nil)" \ + --eval "(setq geiser-scheme-implementation 'guile)" \ + -f org-babel-tangle \ + || rm -f web/client/with-cache.scm + +$(srcdir)/doc/web-client-with-cache.texi: web-client-with-cache.org + $(AM_V_GEN) $(EMACS) --batch \ + --file $(srcdir)/$< \ + --eval "(setq org-confirm-babel-evaluate nil)" \ + --eval "(setq geiser-scheme-implementation 'guile)" \ + -f org-texinfo-export-to-texinfo + @mv web-client-with-cache.texi doc/web-client-with-cache.texi diff --git a/NEWS b/NEWS new file mode 100644 index 0000000..ccac0f2 --- /dev/null +++ b/NEWS @@ -0,0 +1,7 @@ +-*- mode: org; coding: utf-8; -*- + +#+TITLE: Web-Client-With-Cache NEWS – history of user-visible changes +#+STARTUP: content hidestars + +* Publication at 0.0.0 +The code for the main function is written. diff --git a/README b/README new file mode 100644 index 0000000..c031db8 --- /dev/null +++ b/README @@ -0,0 +1,7 @@ +-*- mode: org; coding: utf-8; -*- + +#+TITLE: README for Web-Client-With-Cache + +This project is contained in the Org notebook named +web-client-with-cache.org. You should definitely read that one. + diff --git a/bootstrap b/bootstrap new file mode 100755 index 0000000..11f3413 --- /dev/null +++ b/bootstrap @@ -0,0 +1,7 @@ +#!/bin/sh + +(echo '\input texinfo' ; + echo '@include version.texi') \ + > doc/web-client-with-cache.texi || exit 1 +autoreconf -vif || exit 1 +rm doc/web-client-with-cache.texi || exit 1 diff --git a/configure.ac b/configure.ac new file mode 100644 index 0000000..3ec536c --- /dev/null +++ b/configure.ac @@ -0,0 +1,13 @@ +dnl -*- Autoconf -*- + +AC_INIT([web-client-with-cache], [0.0.0], [vivien@planete-kraus.eu]) +AC_CONFIG_SRCDIR([web-client-with-cache.org]) +AM_INIT_AUTOMAKE([subdir-objects]) +AM_SILENT_RULES([yes]) +AM_MISSING_PROG([EMACS], [emacs]) +GUILE_PKG([3.0 2.2 2.0]) +GUILE_PROGS +GUILE_SITE_DIR +AC_CONFIG_FILES([Makefile]) +AC_CONFIG_FILES([pre-inst-env], [chmod +x pre-inst-env]) +AC_OUTPUT diff --git a/doc/fdl.texi b/doc/fdl.texi new file mode 100644 index 0000000..eaf3da0 --- /dev/null +++ b/doc/fdl.texi @@ -0,0 +1,505 @@ +@c The GNU Free Documentation License. +@center Version 1.3, 3 November 2008 + +@c This file is intended to be included within another document, +@c hence no sectioning command or @node. + +@display +Copyright @copyright{} 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. +@uref{https://fsf.org/} + +Everyone is permitted to copy and distribute verbatim copies +of this license document, but changing it is not allowed. +@end display + +@enumerate 0 +@item +PREAMBLE + +The purpose of this License is to make a manual, textbook, or other +functional and useful document @dfn{free} in the sense of freedom: to +assure everyone the effective freedom to copy and redistribute it, +with or without modifying it, either commercially or noncommercially. +Secondarily, this License preserves for the author and publisher a way +to get credit for their work, while not being considered responsible +for modifications made by others. + +This License is a kind of ``copyleft'', which means that derivative +works of the document must themselves be free in the same sense. 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A copy of the license is included in the section entitled ``GNU + Free Documentation License''. +@end group +@end smallexample + +If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, +replace the ``with@dots{}Texts.''@: line with this: + +@smallexample +@group + with the Invariant Sections being @var{list their titles}, with + the Front-Cover Texts being @var{list}, and with the Back-Cover Texts + being @var{list}. +@end group +@end smallexample + +If you have Invariant Sections without Cover Texts, or some other +combination of the three, merge those two alternatives to suit the +situation. + +If your document contains nontrivial examples of program code, we +recommend releasing these examples in parallel under your choice of +free software license, such as the GNU General Public License, +to permit their use in free software. + +@c Local Variables: +@c ispell-local-pdict: "ispell-dict" +@c End: diff --git a/pre-inst-env.in b/pre-inst-env.in new file mode 100644 index 0000000..844cf1e --- /dev/null +++ b/pre-inst-env.in @@ -0,0 +1,15 @@ +#!/bin/sh + +abs_top_srcdir="$(cd "@abs_top_srcdir@" > /dev/null; pwd)" +abs_top_builddir="$(cd "@abs_top_builddir@" > /dev/null; pwd)" + +export GUILE_LOAD_COMPILED_PATH="$abs_top_builddir${GUILE_LOAD_COMPILED_PATH:+:}$GUILE_LOAD_COMPILED_PATH" +export GUILE_LOAD_PATH="$abs_top_builddir:$abs_top_srcdir${GUILE_LOAD_PATH:+:}:$GUILE_LOAD_PATH" +export "XDG_DATA_HOME=$abs_top_builddir/xdg-data-home" +export "XDG_CACHE_HOME=$abs_top_builddir/xdg-cache-home" +mkdir -p "$XDG_DATA_HOME" +mkdir -p "$XDG_CACHE_HOME" +export GUILE_LOAD_COMPILED_PATH="$abs_top_builddir:$GUILE_LOAD_COMPILED_PATH" +export GUILE_LOAD_PATH="$abs_top_builddir:$abs_top_srcdir:$GUILE_LOAD_PATH" +export GUILE_AUTO_COMPILE=0 +exec "$@" diff --git a/web-client-with-cache.org b/web-client-with-cache.org new file mode 100644 index 0000000..17d3f4f --- /dev/null +++ b/web-client-with-cache.org @@ -0,0 +1,542 @@ +#+title: Web Client with Cache {{{version}}} +#+subtitle: for version {{{version}}}, {{{updated}}} +#+author: Vivien Kraus +#+email: vivien@planete-kraus.eu +#+options: ':t toc:t author:t email:t +#+language: en + +#+macro: version @@texinfo:@value{VERSION}@@ +#+macro: updated @@texinfo:@value{UPDATED}@@ +#+texinfo_filename: web-client-with-cache.info +#+texinfo_header: @syncodeindex pg cp fn +#+texinfo_dir_category: The Algorithmic Language Scheme +#+texinfo_dir_title: Web Client with Cache: (web-client-with-cache) +#+texinfo_dir_desc: Using the cache +#+texinfo_printed_title: Web Client with Cache + +This manual is for the Guile Web Client with Cache (version +{{{version}}}, {{{updated}}}). + +* Copying + :PROPERTIES: + :COPYING: t + :END: +This manual is for the Guile Web Client with Cache. + +Copyright \copy 2021 Vivien Kraus. + +#+begin_quote +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with no +Invariant Sections, with no Front-Cover Texts, and with no Back-Cover +Texts. A copy of the license is included in the section entitled "GNU +Free Documentation License". + +The program present in this document is free software: you can +redistribute it and/or modify it under the terms of the GNU General +Public License as published by the Free Software Foundation, either +version 3 of the License, or (at your option) any later version. + +This program is distributed in the hope that it will be useful, but +WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +General Public License for more details. + +You should have received a copy of the GNU General Public License +along with this program. If not, see [[https://www.gnu.org/licenses/]]. +#+end_quote + +* Using the cache +#+cindex: using the cache + +The API is defined in the =(web client with-cache)= module. It +consists of one function: + +#+begin_src emacs-lisp :noweb yes :exports results :results drawer + (format " + ,#+begin_export texinfo + @defun with-cache [#:http-get] [#:current-time] [#:box] + <> + @end defun + ,#+end_export") +#+end_src + +* Covoiturage +The goal here is to wrap an expensive long-running pure function so +that calling it multiple times with the same arguments until it has +not returned reuses the return value. The name is not pretty, if you +find a better one please tell me. + +#+name: covoiturage-docstring +#+caption: Docstring of the covoiturage function +#+begin_src texinfo + Wrap @var{f} so that simultaneous calls use the same return value. By + simultaneous, we mean parallel calls with the same value for the first + argument (compared with @code{equal?}) during the long-running + evaluation of @var{f}. + + @var{f} takes at least one argument, the key. @var{f} may throw or + return. It is executed in a Future (from @code{(ice-9 futures)}, so + side effects should be synchronized somehow. +#+end_src + +Internally, we use an atomic box. The atomic box contains an alist +from key values to promises to futures. Futures are cool, but once +they are constructed they start running immediately. + +However, if the lockless synchronization failed because of a +concurrent update (for instance, inserting a new query), we should not +start f at all before having updated the atomic box. Otherwise, for +http-get, an unwanted connection to the server will still be +attempted. + +To work around that, we use a promise to a future, so the +future starts when the promise is forced -- thus, either by our +thread, after we have synchronized the box ourselves; or by another +thread, because it has already been added to the box. + +Once the function has returned, we notify all the other waiting +threads and remove everything from the box. Function +[[fn-covoiturage-remove]] does the removal. + +#+name: fn-covoiturage-remove +#+caption: Remove a completed entry from a box +#+begin_src scheme :eval no + (define (remove box key) + (let* ((old (atomic-box-ref box)) + (new (filter (lambda (record) + (not (equal? (car record) key))) + old)) + (discarded + (atomic-box-compare-and-swap! box old new))) + (unless (eq? discarded old) + (remove box key)))) +#+end_src + +The application of function /f/ may either return (multiple values), +or throw. We want to forward both cases to all the callers, so we need +to intercept the throws. Function [[fn-covoiturage-wrap-f]] does that: +call f, and cons either ='ok= or ='error= and the return or throw +values. + +#+name: fn-covoiturage-wrap-f +#+caption: Wrap a thunk so that we know whether it threw or returned +#+begin_src scheme :eval no + (define (wrap-f f) + (catch #t + (lambda () + (call-with-values f + (lambda args + (cons 'ok args)))) + (lambda error + (cons 'error error)))) +#+end_src + +Symmetrically, when we want to report the value, we need to apply +either =throw= or =values=. This is the job of [[fn-covoiturage-report]]. + +#+name: fn-covoiturage-report +#+caption: Report the computed values +#+begin_src scheme :eval no + (define (report result) + (case (car result) + ((ok) (apply values (cdr result))) + ((error) (apply throw (cdr result))))) +#+end_src + +There are now two cases when we query a key: either there is an entry +in the cache, in which case we just remove that, or we need to create +a new future. Function [[fn-covoiturage-create]] will create the job (it +will not start until it has been added to the cache). We note that if +the return value should be cached for longer, the caching should +happen before /f/ has finished executing. + +#+name: fn-covoiturage-create +#+caption: Create a new job (don't start it yet) +#+begin_src scheme :eval no + (define (create box key f args) + (delay + (make-future + (lambda () + (let ((ret (wrap-f (lambda () (apply f key args))))) + (remove box key) + ret))))) +#+end_src + +The query function works atomically: it first reads the cache, use it +if it is present, and otherwise add an entry with a job and start the +job. If it can't do that atomically, it retries. That's function +[[fn-covoiturage-do-query]]. + +#+name: fn-covoiturage-do-query +#+caption: Do query the cache +#+begin_src scheme :eval no + (define (do-query box f key args) + (let ((old (atomic-box-ref box))) + (if (assoc-ref old key) + (report (touch (force (assoc-ref old key)))) + (let* ((job (create box key f args)) + (new (acons key job old))) + (let ((discarded + (atomic-box-compare-and-swap! box old new))) + (if (eq? discarded old) + ;; The box is updated, so the future can be + ;; forced and f starts running + (report (touch (force job))) + ;; Concurrent update, retry. + (do-query box f key args))))))) +#+end_src + +Finally, we wrap everything in a public function that will manage the +state (the atomic box). The final function is [[fn-covoiturage]]. + +#+name: fn-covoiturage +#+caption: The final function definition +#+begin_src scheme :eval no :noweb no-export + (define-public (covoiturage f) + "\ + <>" + (let ((box (make-atomic-box '()))) + <> + <> + <> + <> + <> + (lambda (key . args) + (do-query box f key args)))) +#+end_src + +* Web caching +While we still use an atomic box for this cache, it is more complex +than covoiturage. We need to fix HTTP headers, parse the responses, +manipulate time. + +** Filter =#:header= keyword argument + +Let's start with the headers. We need a function to parse keyword +arguments, extract the non-ignored headers and the non-header keyword +arguments. The function [[fn-filter-keyword]] extracts the headers, and +[[fn-filter-headers]] removes the unwanted ones. + +#+name: fn-filter-keyword +#+caption: Filter a keyword from a keyword list +#+begin_src scheme :eval no + (define (filter-keyword kw args) + (define (search args-kept value args) + (if (null? args) + (values value (reverse args-kept)) + (let ((next-keyword (car args)) + (next-value (cadr args)) + (rest (cddr args))) + (if (eq? next-keyword kw) + (search args-kept (or value next-value) rest) + (search + ;; args-kept is in reverse order! + (cons* next-value next-keyword args-kept) + value + rest))))) + (search '() #f args)) +#+end_src + +#+name: fn-filter-headers +#+caption: Remove headers for which we have the responsibility +#+begin_src scheme :eval no + (define (filter-headers headers) + (filter (lambda (header) + (case (car header) + ((if-none-match if-modified-since) #f) + (else #t))) + headers)) +#+end_src + +** Time management + +Now, it's time for time management. We need different auxiliary +functions: +1. Add seconds to a date, which is polymorphic enough to allow SRFI-19 + dates and SRFI-19 times; +2. Compare two dates or times. + +*** Adding seconds to a date +Function [[fn-date-add]] adds a number of seconds to a time or a date, and +returns a date. + +#+name: fn-date-add +#+caption: Add seconds to a date +#+begin_src scheme :eval no + (define (date-add date seconds) + (let* ((duration (make-time time-duration 0 seconds)) + (time (if (time? date) + date + (date->time-utc date))) + (result (add-duration time duration))) + (time-utc->date result))) +#+end_src + +*** Compare two dates/times +This is the job of functon [[fn-date-geqp]]. If the arguments are dates, +they are first compared to times. + +#+name: fn-date-geqp +#+caption: Compare two dates +#+begin_src scheme :eval no + (define (date>=? past future) + (when (date? past) + (set! past (date->time-utc past))) + (when (date? future) + (set! future (date->time-utc future))) + (time>=? past future)) +#+end_src + +** Fix the responses +There are different things we need to do to responses: +1. Add a date to every response that does not have one; +2. Estimate an expiration date for a response, based on either the + Expires header or its Date and Cache-Control information; +3. Merge the headers for two responses. + +*** Ensure that a response has a date +If the server did not set a date, we set it from the client +clock. This is the job of [[fn-response-with-date]]. + +#+name: fn-response-with-date +#+caption: Ensure that the response has a date. Use the client clock if needed. +#+begin_src scheme :eval no + (define (response-with-date response current-time) + ;; current-time is only used if response does not have a date. + (let ((date (response-date response (time-utc->date current-time))) + (other-headers + (filter (lambda (header) + (not (eq? (car header) 'date))) + (response-headers response)))) + (build-response + #:version (response-version response) + #:code (response-code response) + #:reason-phrase (response-reason-phrase response) + #:headers (acons 'date date other-headers) + #:port (response-port response)))) +#+end_src + +*** Estimate the expiration date from the response +The expiration date can be: +- the max-age value of the cache control after the response date, if + the cache control is present and has a max-age; +- the value of the Expires header; +- =#f= if the others failed. + +This is what [[fn-estimate-response-expires]] does. + +#+name: fn-estimate-response-expires +#+caption: Estimate the expiration date of a response +#+begin_src scheme :eval no + (define (estimate-response-expires response) + (let ((cache-control (response-cache-control response '())) + (expires (response-expires response)) + (date (response-date response))) + (let ((max-age (assoc-ref cache-control 'max-age))) + (cond (max-age + (date-add date max-age)) + (expires expires) + (else #f))))) +#+end_src + +*** Merge the headers of two responses +The difficult part is that this will happen every time a response is +refreshed from a 304 Not Modified response. So if we just merge the +alists, the header alist will grow arithmetically. The trick is to +use a hash table to remove duplicate header names. This explains +function [[fn-merge-headers]]. + +#+name: fn-merge-headers +#+caption: Merge the headers for two responses +#+begin_src scheme :eval no + (define (merge-headers most-important less-important) + (let ((h+ (response-headers most-important)) + (h- (response-headers less-important))) + (let* ((alist (append h+ h-)) + (table (alist->hash-table alist))) + (hash-table->alist table)))) +#+end_src + +** Wrap =http-fetch= so as to store the response +Now we can start using the =covoiturage= function. The inner function +will call =http-get=, but between the moment we have the response and +response body and the moment we return them, we add them to a web +cache. + +The function [[fn-with-cache-add-to-box]] atomically adds the response and +response-body to the cache, while ensuring there is a Date header. + +#+name: fn-with-cache-add-to-box +#+caption: Add a response and its body to the cache +#+begin_src scheme :eval no + (define (with-cache-add-to-box box key response body current-time) + (set! response (response-with-date response current-time)) + (let* ((old (atomic-box-ref box)) + (new (acons key (cons response body) + (filter + (lambda (cell) + (not (equal? key (car cell)))) + old))) + (discarded (atomic-box-compare-and-swap! box old new))) + (if (eq? discarded old) + (values response body) + (with-cache-add-to-box box key response body current-time)))) +#+end_src + +The function [[fn-with-cache-smart-http-get]] takes more argument than +regular =http-get=. It takes a base response and base response body, +which are the previously cached versions of the response. Then, it +proceeds with =http-get=. If the result is a 304 Not Modified +response, then it updates the cached response with the headers from +the new response and returns the previous response. Also, it updates +the cache just before returning. + +#+name: fn-with-cache-smart-http-get +#+caption: =http-get=, but compare with the previous cached responses +#+begin_src scheme :eval no + (define (with-cache-smart-http-get base-response base-response-body + box current-time http-get key . args) + (receive (response response-body) + (apply http-get key args) + (set! response (response-with-date response current-time)) + (when (and base-response (eq? (response-code response) 304)) + (set! response + (build-response + #:version (response-version base-response) + #:code (response-code base-response) + #:reason-phrase (response-reason-phrase base-response) + #:headers (merge-headers response base-response) + #:port (response-port response))) + (set! response-body base-response-body)) + (with-cache-add-to-box box key response response-body current-time))) +#+end_src + +We can now wrap =with-cache-smart-http-get= within covoiturage, and +focus on the main function. The main function takes the box, +current-time and smart http-get function within covoiturage, looks up +the response in the cache, and returns it as is if it is still +valid. Otherwise, the smart http-get is called. This is the job of +function [[fn-with-cache-query]]. + +#+name: fn-with-cache-query +#+caption: The main function for the cache +#+begin_src scheme :eval no + (define (with-cache-query box current-time smart-http-get http-get key . args) + (let* ((old (atomic-box-ref box)) + (resp (assoc-ref old key))) + (receive (request-headers other-request-args) + (filter-keyword #:headers args) + (unless request-headers + (set! request-headers '())) + (set! request-headers (filter-headers request-headers)) + (if resp + (let ((response (car resp)) + (response-body (cdr resp))) + (let ((expires (estimate-response-expires response))) + (if (and expires (date>=? expires current-time)) + ;; The response is cached and not expired + (values response response-body) + ;; The response is cached but expired + (let ((etag (response-etag response)) + (last-modified (response-last-modified response))) + (when etag + (set! request-headers + (acons 'if-none-match (list etag) request-headers))) + (when last-modified + (set! request-headers + (acons 'if-modified-since last-modified request-headers))) + (apply smart-http-get + response response-body box current-time http-get key + #:headers request-headers + other-request-args))))) + ;; The response is not cached + (apply smart-http-get + #f #f box current-time http-get key + #:headers request-headers + other-request-args))))) +#+end_src + +** Putting everything together +The final function is [[fn-with-cache]]. It takes its docstring from +[[with-cache-docstring]]. + +#+name: with-cache-docstring +#+caption: Docstring of the http-get with cache +#+begin_src texinfo + Call @var{http-get} with a cache. @var{http-get} is a procedure that + takes an URI, and optionally some headers and other arguments, and + either fails or returns two values: a response and a response body. + + The following headers are set by the caching function and are thus + ignored from the additional arguments: + + @itemize + @item @code{If-None-Match} + @item @code{If-Modified-Since} + @end itemize + + For cache validation without connecting to the server, + @var{current-time} is needed. It should be a SRFI-19 time or date. By + default, use the client system clock. + + The returned function takes the same arguments as @var{http-get} from + @code{(web client)}, and also returns a response and a response body, + however some headers are filtered, and responses with 304 will be + converted to 200 with the help of the cache, if there is some. + + The optional argument @code{#:box} can be used to use a specific + atomic box instead of one created just for the occasion. +#+end_src + +#+name: fn-with-cache +#+caption: HTTP GET with cache +#+begin_src scheme :eval no :noweb no-export :tangle web/client/with-cache.scm :mkdirp t + (define-module (web client with-cache) + #:use-module (web client) + #:use-module (web response) + #:use-module (srfi srfi-1) + #:use-module (srfi srfi-19) + #:use-module (srfi srfi-69) + #:use-module (ice-9 atomic) + #:use-module (ice-9 receive) + #:use-module (ice-9 optargs) + #:use-module (ice-9 threads) + #:use-module (ice-9 futures)) + + <> + + (define*-public (with-cache + #:key + (http-get http-get) + (current-time current-time) + (box #f)) + "\ + <>" + (let ((box (or box (make-atomic-box '())))) + <> + <> + <> + <> + <> + <> + <> + <> + <> + (define smart-http-get + (covoiturage with-cache-smart-http-get)) + <> + (lambda (uri . args) + (apply with-cache-query box (current-time) smart-http-get http-get uri args)))) +#+end_src + +* GNU Free Documentation License + :PROPERTIES: + :APPENDIX: t + :END: +#+texinfo: @include fdl.texi +* Index + :PROPERTIES: + :INDEX: cp + :END: -- cgit v1.2.3