vole
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A free and open-source forge that lives in your Git repo.
| 1 | package web |
| 2 | |
| 3 | // What one page reads twice. |
| 4 | // |
| 5 | // A page and its header are built from the same facts: the repository, how many |
| 6 | // issues and change requests are open, and the change requests themselves. Each |
| 7 | // of those reads is git work, and the metadata branch grows with the number of |
| 8 | // issues and changes, so asking for the same list twice is the difference |
| 9 | // between a page that costs one read and one that costs two. |
| 10 | // |
| 11 | // The memo is per request and only for reads. A request that writes metadata |
| 12 | // answers with a redirect, so it has nothing to memoise and cannot be served a |
| 13 | // list it just invalidated; the next request sees the write. Nothing is cached |
| 14 | // across requests, which is why a push is visible on the next page load without |
| 15 | // a hook, a TTL, or an invalidation protocol. |
| 16 | |
| 17 | import ( |
| 18 | "context" |
| 19 | "fmt" |
| 20 | "net/http" |
| 21 | "sync" |
| 22 | |
| 23 | "rodent.software/vole/forge/index" |
| 24 | "rodent.software/vole/forge/repo" |
| 25 | "rodent.software/vole/metadata" |
| 26 | ) |
| 27 | |
| 28 | // memoKey is the context key for the request's memo. It is a private type so no |
| 29 | // other package can install a value under it. |
| 30 | type memoKey struct{} |
| 31 | |
| 32 | type memoCounts struct { |
| 33 | issues, requests int |
| 34 | } |
| 35 | |
| 36 | type memoRequests struct { |
| 37 | list []*metadata.Request |
| 38 | err error |
| 39 | } |
| 40 | |
| 41 | // memoHead is the metadata branch's commit as resolved for this request. The |
| 42 | // index and the request list both need it, and it cannot move under a read |
| 43 | // request without a push arriving mid-render. |
| 44 | type memoHead struct { |
| 45 | sha string |
| 46 | err error |
| 47 | } |
| 48 | |
| 49 | type requestMemo struct { |
| 50 | mu sync.Mutex |
| 51 | repos map[string]*repo.Meta |
| 52 | counts map[string]memoCounts |
| 53 | lists map[string]memoRequests |
| 54 | ensured map[string]error |
| 55 | heads map[string]memoHead |
| 56 | } |
| 57 | |
| 58 | func newRequestMemo() *requestMemo { |
| 59 | return &requestMemo{ |
| 60 | repos: map[string]*repo.Meta{}, |
| 61 | counts: map[string]memoCounts{}, |
| 62 | lists: map[string]memoRequests{}, |
| 63 | ensured: map[string]error{}, |
| 64 | heads: map[string]memoHead{}, |
| 65 | } |
| 66 | } |
| 67 | |
| 68 | // withMemo gives a read request one memo. A mutating request gets none: it may |
| 69 | // have just changed what it would be reading. |
| 70 | func withMemo(r *http.Request) *http.Request { |
| 71 | if r.Method != http.MethodGet && r.Method != http.MethodHead { |
| 72 | return r |
| 73 | } |
| 74 | return r.WithContext(context.WithValue(r.Context(), memoKey{}, newRequestMemo())) |
| 75 | } |
| 76 | |
| 77 | // memoOf returns the request's memo, or nil when the request has none. Callers |
| 78 | // treat nil as "read it directly", so a helper can be used from a write handler |
| 79 | // that has no memo. |
| 80 | func memoOf(r *http.Request) *requestMemo { |
| 81 | memo, _ := r.Context().Value(memoKey{}).(*requestMemo) |
| 82 | return memo |
| 83 | } |
| 84 | |
| 85 | // repo opens a repository by name, once per request. Opening it resolves HEAD's |
| 86 | // branch with a git call, and a page opens the same repository for its header, |
| 87 | // its body and its ACL: the same fact does not need three processes. |
| 88 | func (w *Web) repo(memo *requestMemo, name string) (*repo.Meta, error) { |
| 89 | if memo != nil { |
| 90 | memo.mu.Lock() |
| 91 | m, ok := memo.repos[name] |
| 92 | memo.mu.Unlock() |
| 93 | if ok { |
| 94 | return m, nil |
| 95 | } |
| 96 | } |
| 97 | m, err := w.Repos.Open(name) |
| 98 | if err != nil { |
| 99 | return nil, err |
| 100 | } |
| 101 | if memo != nil { |
| 102 | memo.mu.Lock() |
| 103 | memo.repos[name] = m |
| 104 | memo.mu.Unlock() |
| 105 | } |
| 106 | return m, nil |
| 107 | } |
| 108 | |
| 109 | // metadataHead resolves the metadata branch once per request. Both the index |
| 110 | // refresh and the change-request read start by resolving it, and a page needs |
| 111 | // both. |
| 112 | func (w *Web) metadataHead(memo *requestMemo, m *repo.Meta) (string, error) { |
| 113 | if memo == nil { |
| 114 | return m.Git().RefCommit(metadata.Ref) |
| 115 | } |
| 116 | memo.mu.Lock() |
| 117 | h, ok := memo.heads[m.Name] |
| 118 | memo.mu.Unlock() |
| 119 | if ok { |
| 120 | return h.sha, h.err |
| 121 | } |
| 122 | sha, err := m.Git().RefCommit(metadata.Ref) |
| 123 | memo.mu.Lock() |
| 124 | memo.heads[m.Name] = memoHead{sha: sha, err: err} |
| 125 | memo.mu.Unlock() |
| 126 | return sha, err |
| 127 | } |
| 128 | |
| 129 | // ensureIndex refreshes the rows the repository derives from its metadata branch |
| 130 | // at most once per request. Every surface that shows a number or a count asks |
| 131 | // for it, and the refresh starts with a git call to see whether the branch |
| 132 | // moved: the header, the issue list and the number in a URL should not each pay |
| 133 | // for the same check on one page. |
| 134 | func (w *Web) ensureIndex(memo *requestMemo, m *repo.Meta) error { |
| 135 | if memo == nil { |
| 136 | return w.Index.Ensure(m) |
| 137 | } |
| 138 | memo.mu.Lock() |
| 139 | err, ok := memo.ensured[m.Name] |
| 140 | memo.mu.Unlock() |
| 141 | if ok { |
| 142 | return err |
| 143 | } |
| 144 | head, err := w.metadataHead(memo, m) |
| 145 | if err == nil { |
| 146 | err = w.Index.EnsureAt(m, head) |
| 147 | } |
| 148 | memo.mu.Lock() |
| 149 | memo.ensured[m.Name] = err |
| 150 | memo.mu.Unlock() |
| 151 | return err |
| 152 | } |
| 153 | |
| 154 | // requestsAt returns the change requests on the metadata branch, reading them |
| 155 | // once per request. The list is the whole branch, so the header's open count and |
| 156 | // the page's rows share one read rather than paying for the tree twice. |
| 157 | func (w *Web) requestsAt(memo *requestMemo, m *repo.Meta) ([]*metadata.Request, error) { |
| 158 | if memo == nil { |
| 159 | return metadata.LoadRequests(m.Git(), metadata.Ref) |
| 160 | } |
| 161 | memo.mu.Lock() |
| 162 | entry, ok := memo.lists[m.Name] |
| 163 | memo.mu.Unlock() |
| 164 | if ok { |
| 165 | return entry.list, entry.err |
| 166 | } |
| 167 | head, err := w.metadataHead(memo, m) |
| 168 | var list []*metadata.Request |
| 169 | if err == nil { |
| 170 | list, err = metadata.LoadRequestsAt(m.Git(), head) |
| 171 | } |
| 172 | memo.mu.Lock() |
| 173 | memo.lists[m.Name] = memoRequests{list: list, err: err} |
| 174 | memo.mu.Unlock() |
| 175 | return list, err |
| 176 | } |
| 177 | |
| 178 | // requestAt returns one change request for rendering. A read request uses the |
| 179 | // index, which ensureIndex refreshes to the branch's current commit. A write |
| 180 | // request reads git instead: it has no memo because it may have just changed the |
| 181 | // record, and it must not be answered by the version it replaced. |
| 182 | func (w *Web) requestAt(memo *requestMemo, m *repo.Meta, id string) (*metadata.Request, error) { |
| 183 | if w.Index != nil && memo != nil { |
| 184 | if err := w.ensureIndex(memo, m); err != nil { |
| 185 | return nil, err |
| 186 | } |
| 187 | return w.Index.Request(m.ID, id) |
| 188 | } |
| 189 | head, err := w.metadataHead(memo, m) |
| 190 | if err != nil { |
| 191 | return nil, err |
| 192 | } |
| 193 | req, found, err := metadata.LoadRequestAt(m.Git(), head, id) |
| 194 | if err != nil { |
| 195 | return nil, err |
| 196 | } |
| 197 | if !found { |
| 198 | return nil, fmt.Errorf("requests: no request %s", id) |
| 199 | } |
| 200 | return req, nil |
| 201 | } |
| 202 | |
| 203 | // issueAt returns one issue for rendering, on the same rule: the index for a |
| 204 | // read request, git for a write or a Web without an index. |
| 205 | func (w *Web) issueAt(memo *requestMemo, m *repo.Meta, id string) (*metadata.Issue, error) { |
| 206 | if w.Index != nil && memo != nil { |
| 207 | if err := w.ensureIndex(memo, m); err != nil { |
| 208 | return nil, err |
| 209 | } |
| 210 | return w.Index.Issue(m.ID, id) |
| 211 | } |
| 212 | return index.LoadIssue(m, id) |
| 213 | } |
| 214 |