Tx (change) output splitter

[antiochp]

This PR lets us specify an (optional) number of change outputs to generate when building a transaction via grin wallet send via --change_outputs=2.

If this is not specified then we default to 1 single change output as per current behavior.

The primary motivation for this was to have an easy way of generating a bunch of test data (unspent outputs) that can then be used to test large txs and large blocks etc.

../target/release/grin wallet send --help   
grin-wallet-send 
Builds a transaction to send coins and sends it to the specified listener directly.

USAGE:
    grin wallet send [FLAGS] [OPTIONS] [amount]

FLAGS:
    -f, --fluff      Fluff the transaction (ignore Dandelion relay protocol)
    -h, --help       Prints help information
    -V, --version    Prints version information

OPTIONS:
    -o, --change_outputs <change_outputs>     Number of change outputs to generate (mainly for testing). [default: 1]
    -d, --dest <dest>                         Send the transaction to the provided server
    -c, --min_conf <minimum_confirmations>    Minimum number of confirmations required for an output to be spendable.
                                              [default: 1]
    -s, --selection <selection_strategy>      Coin/Output selection strategy. [default: all]  [possible values: all,
                                              smallest]

ARGS:
    <amount>    Number of coins to send with optional fraction, e.g. 12.423

Generating a tx with a single change output looks something like this -

../target/release/grin wallet send 1.0 --fluff -d "http://127.0.0.1:13415" --change_outputs 1
...
Aug 17 15:45:52.955 DEBG Refreshing wallet outputs
Aug 17 15:45:53.673 DEBG Building input (spending coinbase): 60000000000, 8190a17d03ad020ffa6a
Aug 17 15:45:53.673 DEBG Building input (spending coinbase): 60408000000, 73a344933aba24fccfc8
Aug 17 15:45:53.673 DEBG Building change outputs: total change: 119401000000 (1 outputs)
Aug 17 15:45:53.766 DEBG Building an output: 119401000000, Commitment(081fbc77ad3e806618c36d6148b73aae396878bac5499258375b909ba60f97c3b4)
Aug 17 15:45:53.824 DEBG Posting transaction slate to http://127.0.0.1:13415/v1/wallet/foreign/receive_tx
Aug 17 15:45:54.043 DEBG Validating final transaction
Aug 17 15:45:54.056 INFO Tx created: 1.000000000 grin to http://127.0.0.1:13415 (strategy 'all')
Aug 17 15:45:54.139 INFO Tx sent

Aug 17 15:45:54.115 INFO Pushing transaction with 2 inputs and 2 outputs to pool.
Aug 17 15:45:54.115 DEBG pool: add_to_pool: a1c6afaa, kernels - 1, stem? false
Aug 17 15:45:54.127 DEBG pool [txpool]: add_to_pool: a1c6afaa, TxSource { debug_name: "push-api", identifier: "?.?.?.?" }

Generating a tx with a large number of change outputs looks like this -

../target/release/grin wallet send 1.0 --fluff -d "http://127.0.0.1:13415" --change_outputs 51
...
Aug 17 15:50:41.101 DEBG Refreshing wallet outputs
Aug 17 15:50:41.914 DEBG Building input (spending coinbase): 60000000000, ad60d899d35cb61e174a
Aug 17 15:50:41.914 DEBG Building change outputs: total change: 58792000000 (51 outputs)
Aug 17 15:50:42.039 DEBG Building an output: 1152784313, Commitment(099ed55f0043f0745d158aeefbd869e833d00b182ccd90875f70280257c5fc663f)
Aug 17 15:50:42.189 DEBG Building an output: 1152784313, Commitment(0866d9afe100b16beb898a7eb465a8b320b7ae600484309d55e3218c091bbd45dd)
Aug 17 15:50:42.314 DEBG Building an output: 1152784313, Commitment(08e161226855ad0a4b7ea510c8d4e180e71e73f8cdb628be86bd21f73f64cbbeaa)
Aug 17 15:50:42.438 DEBG Building an output: 1152784313, Commitment(084c2cb6ad4547ae975eaeeecba22f079fa811aa0ef54bd037f099ff080d9167b6)
Aug 17 15:50:42.565 DEBG Building an output: 1152784313, Commitment(0834a9624b5b75a3ba667099a6b4249dd18add2b473f10053676cb7e31944129fd)
Aug 17 15:50:42.690 DEBG Building an output: 1152784313, Commitment(087144dce0aa9a7c97141eeaccab0fe3933b13d128d66b3175aadb88465582b641)
Aug 17 15:50:42.816 DEBG Building an output: 1152784313, Commitment(09cd98a2866ba1a778b60155a88e1ad72af566036dd61c550e20cdf0b44070b94c)
Aug 17 15:50:42.941 DEBG Building an output: 1152784313, Commitment(09ec65db8c3b0d4d0f70c5712e6eff43f18b857bada111d855613094cc4fd993fa)
Aug 17 15:50:43.072 DEBG Building an output: 1152784313, Commitment(09eb9e5b21e368234cea4ce21542c8f365ab0a3df4a2cc015b7f1f1911f6110b60)
Aug 17 15:50:43.201 DEBG Building an output: 1152784313, Commitment(09054979b6838ba9d4e913ad69e838213f73063dff1c0c231b2786b583241ca8f2)
Aug 17 15:50:43.328 DEBG Building an output: 1152784313, Commitment(09eae3308872dc9e7b943c008fa1ec19956620fcf3c2d8e5e432cc3b7d1d5963ba)
Aug 17 15:50:43.465 DEBG Building an output: 1152784313, Commitment(08bb6a47b4bb11b01424d181970e25c6320a7e3740269b0560349bc02000288c16)
Aug 17 15:50:43.604 DEBG Building an output: 1152784313, Commitment(085cd2efa8862cb23060a8a283546b669fe725d3ab06d05c39343c8be4f11f7bb8)
Aug 17 15:50:43.755 DEBG Building an output: 1152784313, Commitment(09170096d1d59b6a3cab12c99a022d89f5f1c0ddac883998b8e88e72ff841fd21a)
Aug 17 15:50:43.890 DEBG Building an output: 1152784313, Commitment(084c9d7abc4744c5a3057af12eff444d79f0000471e3969ee500f4aaac3009d905)
Aug 17 15:50:44.027 DEBG Building an output: 1152784313, Commitment(08f9d87a82cc50e44161cb0659f8b9b4ee85be53cb932716babda18e999fbd64e8)
Aug 17 15:50:44.158 DEBG Building an output: 1152784313, Commitment(09dd4d230feaaba4ac2715dc18e91f001fae9216c18ca1f10ab4fb2906acd5c20f)
Aug 17 15:50:44.297 DEBG Building an output: 1152784313, Commitment(08cc5707a7bc95e6e2a460c7a0e1bb598ab28e5f9d4f79469751760db14b255b5e)
Aug 17 15:50:44.434 DEBG Building an output: 1152784313, Commitment(08a6beda9eed2f14b28b582411402470085de38e70b87446afb75b6886aba47239)
Aug 17 15:50:44.572 DEBG Building an output: 1152784313, Commitment(092ab2a95396372509100622f6aded859ab93a5c942c74298529319bf75bd1f804)
Aug 17 15:50:44.709 DEBG Building an output: 1152784313, Commitment(09228d723054cc5d13cfe5ca59c4355981f7cb5e838126c3f7272679caea19cd70)
Aug 17 15:50:44.846 DEBG Building an output: 1152784313, Commitment(086c503fa482633910005deee9971fd0363448e207cc335834472740718b84a92e)
Aug 17 15:50:44.981 DEBG Building an output: 1152784313, Commitment(0954146708c2a6502113c91af5b183d50569125b32cbcde5d1ea79002511d79194)
Aug 17 15:50:45.121 DEBG Building an output: 1152784313, Commitment(084b39014a16cb09306375b833a368a4f9612099b886789a8ffcb93f6674335231)
Aug 17 15:50:45.257 DEBG Building an output: 1152784313, Commitment(0926644d3a799ac4c1341344307b219fe6d6c43b518485c3b7d795707b72b548b2)
Aug 17 15:50:45.399 DEBG Building an output: 1152784313, Commitment(090b75cfc0d557feff074e5d599364c099406e2353e79738344c48374c55d6ad2b)
Aug 17 15:50:45.535 DEBG Building an output: 1152784313, Commitment(09c3a89eca344fc5c68949740963d495b891730de471eb2748dd45b4edf8285d0a)
Aug 17 15:50:45.674 DEBG Building an output: 1152784313, Commitment(086a7aa630dba6055bd8e6d98612b55c5c516af1fd6557eb97c08eb054ea63f14b)
Aug 17 15:50:45.814 DEBG Building an output: 1152784313, Commitment(09fea854170325e40186ac133705a4731f365d3893d80445d11cc212e14b5160bd)
Aug 17 15:50:45.956 DEBG Building an output: 1152784313, Commitment(09fb608da71dcaa80a70728f189eaad87b665ad1f5c0057b710e05d02e7cc92a30)
Aug 17 15:50:46.096 DEBG Building an output: 1152784313, Commitment(08a6dd55373c28a36e2ecc4cb9b6a8a3a80e73ac165c417aa1d4b57c572ef362bc)
Aug 17 15:50:46.240 DEBG Building an output: 1152784313, Commitment(0922bac0c1b6720126b663d54c1af1d8a8d094b16c630ab1d8d079e05efced7d54)
Aug 17 15:50:46.381 DEBG Building an output: 1152784313, Commitment(09ef56c8ef9c448c2a18ed5575fcf26e85ba26aca105f6e86ecf97c493f0d950d5)
Aug 17 15:50:46.520 DEBG Building an output: 1152784313, Commitment(09fb9330fdbd3658b8acb46797ab899e160d56f8760f89cfe92b8772a799700f7e)
Aug 17 15:50:46.660 DEBG Building an output: 1152784313, Commitment(0815ca1d007928cb59cd7a4a95c2984fc3364f8b4e4dfeaf5b630d337433464ad9)
Aug 17 15:50:46.798 DEBG Building an output: 1152784313, Commitment(083138057e6f8a3ec326bc00e672968b427b22df58baabd984019b3d784a532934)
Aug 17 15:50:46.936 DEBG Building an output: 1152784313, Commitment(08c9734b2d142eff08087145e2c6ba16548a77bbf352abe440468c1b314204f77d)
Aug 17 15:50:47.077 DEBG Building an output: 1152784313, Commitment(085f92fbaf4f1d8f9cd82aa18c09dc991266a64ab9006809b7b02e0c2a34c92e17)
Aug 17 15:50:47.217 DEBG Building an output: 1152784313, Commitment(0951fd8168c8fd44e0e9813cb5cad34a37db22fcfa5e6e22ade0f55743089b5064)
Aug 17 15:50:47.356 DEBG Building an output: 1152784313, Commitment(08f3941b456f55f3a9491cfddc79e25d6a6dcf9e9553880ee311ec0f2c0f4517b7)
Aug 17 15:50:47.495 DEBG Building an output: 1152784313, Commitment(09ee3fb40360f173e0086c0d4d9d76d8cebf7f1ce413f706481f7cc0cda8267d83)
Aug 17 15:50:47.633 DEBG Building an output: 1152784313, Commitment(0841dedb34ac5239300c5654f8e7bc040948240d506bc68e41619a9ed73b5025f3)
Aug 17 15:50:47.770 DEBG Building an output: 1152784313, Commitment(09345c4a489d3d67da8edb850578f6910164cf4ed16a9343147c3218b71a4b1ca5)
Aug 17 15:50:47.911 DEBG Building an output: 1152784313, Commitment(089b551684b9c5ca073537dcdce0fb80b4b244c3122781beb1d305e4519fbcf91e)
Aug 17 15:50:48.049 DEBG Building an output: 1152784313, Commitment(0880dde864794266eb3a6ae32120ff65443eb1295ae054313062a5c513e9ea6f11)
Aug 17 15:50:48.193 DEBG Building an output: 1152784313, Commitment(092c6d24c57485afffb13b9cd53090219bf754489e811bfeba871dc57739fec14e)
Aug 17 15:50:48.332 DEBG Building an output: 1152784313, Commitment(09bf6be78e70bc2702eb08daa169e1bec71e4e750f859b063a010c56a2235de3f5)
Aug 17 15:50:48.468 DEBG Building an output: 1152784313, Commitment(08390bf81d76aba4dbdf7286d82fd57037529d0ede1785394002562155d1a75eaa)
Aug 17 15:50:48.611 DEBG Building an output: 1152784313, Commitment(08bacb1bd39aae5cfca95d10ea461742e7d8d004a4e207147018d111f4d208dac2)
Aug 17 15:50:48.750 DEBG Building an output: 1152784313, Commitment(091cb4970dcdc1cc0fdd1feaaad7395bd5c074f6e957fc49618644757be05f3051)
Aug 17 15:50:48.890 DEBG Building an output: 1152784350, Commitment(0950ccb1ac6a7015a52e70cbdcc911a2f2245f2b773032bce2a236b6092f665663)
Aug 17 15:50:48.934 DEBG Posting transaction slate to http://127.0.0.1:13415/v1/wallet/foreign/receive_tx
Aug 17 15:50:49.399 DEBG Validating final transaction
Aug 17 15:50:49.665 INFO Tx created: 1.000000000 grin to http://127.0.0.1:13415 (strategy 'all')
Aug 17 15:50:50.426 INFO Tx sent

Aug 17 15:50:49.921 INFO Pushing transaction with 1 inputs and 52 outputs to pool.
Aug 17 15:50:49.921 DEBG pool: add_to_pool: f3bc9c7f, kernels - 1, stem? false
Aug 17 15:50:50.170 DEBG pool [txpool]: add_to_pool: f3bc9c7f, TxSource { debug_name: "push-api", identifier: "?.?.?.?" }

[antiochp]

You can go pretty wild with this as well, it just takes a while to build the rangeproofs for all the outputs in the tx (~3 mins here for 1,000 outputs and corresponding rangeproofs)...

Aug 17 15:57:18.563 DEBG Refreshing wallet outputs
Aug 17 15:57:19.429 DEBG Building input (spending coinbase): 60000000000, 0aaa9566d7ee848bc4e9
Aug 17 15:57:19.429 DEBG Building change outputs: total change: 54996000000 (1000 outputs)
Aug 17 15:57:20.091 DEBG Building an output: 54996000, Commitment(0950d5ce4704166c8665947f6f37501b4316ebef54f35af841519975a61fe34994)
Aug 17 15:57:20.244 DEBG Building an output: 54996000, Commitment(08a1e05e7ff2b39e4f25e1b7241cc8152817e40e74c86b768c234d79c44bd439e1)
Aug 17 15:57:20.372 DEBG Building an output: 54996000, Commitment(08540a067121e90dcddc45b77d35c088507702ffd17bba34e03e8198bfda9e67f4)
...
Aug 17 16:00:09.783 DEBG Building an output: 54996000, Commitment(08a1a4f197b75deab9eb909a92de512a040ca827565b5e2d0169ffec245e67d67d)
Aug 17 16:00:10.006 DEBG Building an output: 54996000, Commitment(08de1ec4d5a2111a41c3d9f6e34b9390cf0f8b3272fca2ce7a6c887d3106a729cb)
Aug 17 16:00:10.222 DEBG Building an output: 54996000, Commitment(0946c07739a3b387685f709ebd2c71b32319f738467ef12d14b3c6a2451c21fc9f)
Aug 17 16:00:10.410 DEBG Posting transaction slate to http://127.0.0.1:13415/v1/wallet/foreign/receive_tx
Aug 17 16:00:15.365 DEBG Validating final transaction
Aug 17 16:00:20.334 INFO Tx created: 1.000000000 grin to http://127.0.0.1:13415 (strategy 'all')
Aug 17 16:00:34.236 INFO Tx sent

Aug 17 16:00:25.120 INFO Pushing transaction with 1 inputs and 1001 outputs to pool.
Aug 17 16:00:25.121 DEBG pool: add_to_pool: 8edfa463, kernels - 1, stem? false
Aug 17 16:00:29.672 DEBG pool [txpool]: add_to_pool: 8edfa463, TxSource { debug_name: "push-api", identifier: "?.?.?.?" }