Contextアンチパターン

by Seiji Takahashi

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ContextΞϯνύλʔϯ @__timakin__ golang.tokyo#5

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ࣗݾ঺հ

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ࣗݾ঺հ • twitter: @__timakin__ • github: timakin • גࣜձࣾGunosy ৽نࣄۀ։ൃࣨ(Go/Swift) • ओͳGoϥΠϒϥϦ։ൃ෺ • gopli (DBϨϓϦέʔγϣϯπʔϧ) • gonvert (จࣈίʔυม׵ϥΠϒϥϦ) • octop (githubͷissue, PRϏϡʔ༻CLIπʔϧ) • ts (ٕज़ɾϏδωεܥχϡʔε८ճCLIπʔϧ) • ϓϥΠϕʔτͰΫϩʔϥʔ࡞੒ɺ࠷ۙಈը഑৴पΓ͕ؾʹͳͬͯ·͢ɻ

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Copyright© Gunosy Inc. All Rights Reserved 4 Go / Python ΤϯδχΞืूத ▶https://gunosy.co.jp/recruit/ Gunosy͸ɺ౦ژେֶʹ௨͏3ਓͷֶੜͷ  ʮ৘ใΛੈքதͷਓʹ࠷దʹಧ͚͍ͨʯͱ͍͏૝͍͔Β࢝·Γ·ͨ͠ɻ ౦ূϚβʔζ্৔ɺ࿡ຊ໦ώϧζ΁ͷΦϑΟεҠసΛܦͯɺ  େ͖͘੒௕͍ͯ͠ΔձࣾͰ׆༂͍ͨ͠ϝϯόʔΛืू͍ͯ͠·͢ɻ

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ຊ೔ͷओࢫ

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ContextΛ͋͋ͯ͜͠͏ͯͨ͠Β  ΰουΦϒδΣΫτͰ͖ͨ ͢·Μ

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Զ͕Ξϯνύλʔϯͩ ٩( ᐛ )و

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ΞδΣϯμ • context.ContextͷऔΓѻ͍ʹ͍ͭͯ • Ξϯνύλʔϯͷ࣮ྫʢ΍ͬͪΌͬͨʂ٩( ᐛ )وʣ • ެࣜͷGoDocͰਪ঑͞ΕΔίϯηϓτ • ൓লͱվળ

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Ξϯνύλʔϯͷ࣮ྫ

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@GoConference 2017

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͍ͭ͜Λݟͯ͘ΕɺͲ͏ࢥ͏ʁ

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<- echoͷcustom context <- context in context (!!)

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͞Βʹ͍ͭ͜Λݟͯ͘Εʂ

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͍ͭ͜Λݟͯ͘ΕɺͲ͏ࢥ͏ʁ

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͍ͭ͜Λݟͯ͘ΕɺͲ͏ࢥ͏ʁ <- repository in context (!?)

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͏͢͏͢ײ͍ͮͯ͸͍ͨΑʂʂ ̍̍

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͢·ΜͱࢥͬͯΔ ٩( ᐛ )و

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ݴ͍༁

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context(context.Context) in context(ϑϨʔϜϫʔΫͷContext) • echoͷϑϨʔϜϫʔΫͷcontextͰ͸ͳ͘ඪ४ύοέʔδ ͷcontextΛ࢖ͬͯɺ಺෦ͷϩδοΫͰར༻͍ͯ͠Δ  goroutineͷλΠϜΞ΢τ੍ޚΛ͍ͨ͠ • ͕ɺϦΫΤετϋϯυϥʹ౉ͬͯ͘Δͷ͸  echo.Contextͩ͠ɺGAEͩͱhttp.Request͔Β  contextΛऔΓग़ͤͳ͍ɻ • ϋϯυϥʹcontextΛ౉͢ʹ͸echo.Contextʹ  context.ContextΛؚΊɺͦΕΛϋϯυϥҎԼͷ  ϨΠϠʔͰར༻͢Δඞཁ͕͋Δ

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<- echoͷcustom context <- context in context (!!)

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repository in context • ਃ͠։͖͍͟͝·ͤΜʂʂ̍̍  ͍͕ͭ͜ਆͩʂ • ·͊ͿͬͪΌ͚طଘͷ࣮૷(or ࢿྉ)ࢀߟʹ  ࡞ͬͨΜͰ͕͢ɺέʔεόΠέʔεͰɺ  ΘΓͱ͜͏͍͏globalͳΦϒδΣΫτΛೖΕͯΔ  ݹ͍࣮૷ͱ͔͋ͬͯɺਅࣅͪΌͬͨɻ • ඪ४ύοέʔδͱͯ͠૊Έࠐ·ΕΔલͷ࣮૷Ͱ͸  ͜͏͍͏ͷ΋͋ͬͨΑɺ͋ͬͨ͸ͣͳΜͩɻ • ਖ਼௚repository͚ͩ͡Όͳ͘conﬁgͱ͔΋٧ΊͪΌͬͨ

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Ҏ্ʹରͯ͠օ͞Μौ͍൓Ԡ

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ͦ͏͍͑͹GoDocͰ͸

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GoDoc • Package context deﬁnes the Context type,   which carries deadlines, cancelation signals, and other request-scoped values across API boundaries and between processes. • Use context Values only for request-scoped data that transits processes and APIs, not for passing optional parameters to functions. • Do not store Contexts inside a struct type; instead, pass a Context explicitly to each function that needs it. • ͢·Μͯɻ

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GoDoc • ओʹgoroutine͕བྷΉॲཧɺAPIΛ·͙ͨॲཧΛߦ͏࣌ɺ  λΠϜΞ΢τ੍ޚΛద੾ʹߦ͏ͨΊʹ࢖͏ • UserIDɺଞJWT౳ͷɺͦͷϦΫΤετʹݶఆ͞ΕΔ஋ΛGet/Set͢Δ ͱ͖ʹͷΈValueΛ࢖͏ • Go1.7Ҏલ(ࠓͷGAEͱ͔)  func GetHandler(ctx context.Context,   w http.ResponseWriter, r *http.Request)    Go1.7Ҏ߱  ctx := r.Context() • ଞͷ༻్ɺड͚౉͠ํͰ࢖Θͳ͍ɻ  ઈରͩͧɻ

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൓লͱվળ

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GoDoc • ແବʹߏ଄ମʹcontextೖΕͳ͍ • echo -> net/http • ContextΛద੾ʹϋϯυϥʹ౉͢ • λΠϜΞ΢τઃఆ͸ServeHTTPͰߦ͏ʢMiddlewareͰ΋Մʣ • func Handler(ctx context.Context, w http.ResponseWriter, r *http.Request) • request-scopedͳ஋ʹݶఆ • repository.FromContextͱ͔શ෦ফ͢ • ϋϯυϥͰ౎౓ctxΛ౉ͯ͠ੜ੒ • ֤छΫϥΠΞϯτ΍Βlogger͸HandlerͷϨγʔόΛఆٛͯͦ͠ͷதʹೖΕΔ • function (app *App) GetItemHandler(ctx context.Context, …)

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ແବʹߏ଄ମʹcontextೖΕͳ͍ • echoΛnet/httpʹશஔ͖׵͑ • GAE(SE)ͩͱrequestʹContext͕ೖͬͯͳ͍ɻ  ͞Βʹɺecho.ContextͷͲ͔͜Β΋context.Context͕ͱ Γͩͤͳ͍ɻ • ͦ΋ͦ΋GAEΛ࢖͍ͬͯͨͷͰɺechoඋ͑෇͚ͷϩΨʔ ͱ͔࢖Θͳ͍͠ɺrouting͘Β͍Ͱ͔͠Ըܙͳ͍ • ϑϨʔϜϫʔΫ͕଍͔ͤʹͳ͍ͬͯͨͷͰɺ֎͢ɻ • ϋϯυϥʹඪ४ͷcontext͚ͩ౉͢Լ४උɻ

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ContextΛద੾ʹϋϯυϥʹ౉͢ • λΠϜΞ΢τઃఆ͸ServeHTTPͰߦ͏ʢMiddleware Ͱ΋Մʣ ServeHTTPΛ࣮૷ͨ͠AppHandlerΛఆٛͯ͠ɺ  தͰappengineͷContext(context.Context)Λ λΠϜΞ΢τઃఆ෇͖Ͱϋϯυϥʹ౉͢

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request-scopedͳ஋ʹݶఆ • ͔ͯrequest-scopedͳ஋ͱ͔ಛʹͳ͍APIͩͬͨɻ • ͳͷͰWithValueશ෦ফͨ͠ɻ • repository.FromContextͱ͔શ෦ফ͢ • ϋϯυϥͰ౎౓ctxΛ౉ͯ͠ੜ੒ • GAEͩͱloggerͱ͔datastoreͰcontext͕ඞཁ • ͳͷͰɺglobalʹѻ͍͍ͨ஋ͩͱͯ͠΋ɺ  ϋϯυϥҎ߱Ͱຖճݺͼग़ͯ͠·͢ɻ  ʢ͜Ε͸ϕετϓϥΫςΟε͋Δͷ͔ʁʣ

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Ϩγʔόʹglobalͳ஋ΛೖΕΔ

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• (app *App)ΛϨγʔόͱͯ͠ઃఆ͢Δʹ͸handlerʹ ౰ͨΔϝιου͸શͯಉҰpackageͱͯ͠ఆٛ͞ΕΔ ඞཁ͕͋Δ • cannot deﬁne new methods on non-local type • ͳͷͰɺݸผͷυϝΠϯϩδοΫΛ࣋ͭσΟϨΫτϦ ͱ͸ผʹɺhandlerσΟϨΫτϦΛஔ͖ɺͦ͜ʹApp ͷఆٛͱݸผͷϦΫΤετϋϯυϥΛ࣋ͨͤΔɻ Ϩγʔόʹglobalͳ஋ΛೖΕΔ

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app.go

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main.go handler.AppHandler{Impl: app.HogeHandler}  ͱ͍͏ܗࣜͰɺServeHTTPΛ࣋ͭAppHandlerʹ App structΛ࣋ͭHogeHandlerΛ౉͢ɻ

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·ͱΊ • ਆ͸ࢮΜͩɻcontextড়Խ׬ྃɻ • request-scopedͳ஋ͱɺλΠϜΞ΢τҎ֎࢖Θͳ͍ɻ • άϩʔόϧͳΦϒδΣΫτΛར༻͢ΔͨΊʹ  ϋϯυϥڞ௨ͷstructΛ༻ҙ͢Δɻ  ͦͷӨڹͰϋϯυϥ͸ಉҰpackageʹ·ͱΊΔɻ